Central Idea

Find the central idea
The term "machine gun" is commonly applied to any gun that is designed to fire repeatedly and in rapid succession for as long as the trigger is held down.  During the course of warfare, the trigger of some machine guns may be held down almost continuously for hours to create suppressant fire (rounds fired not necessarily to kill an enemy, but to prevent them from attacking).  All of this firing can generate a lot of heat, which may cause the weapon to overheat and malfunction.  But this situation has been addressed in a number of ways.  For one, practically all machine guns fire from an open bolt, which allows air to cool the breach between bursts of fire.  Additionally, some machine guns have removable barrels, which allow hot barrels to be replaced.  And some advanced machine guns even have sophisticated barrel cooling systems, which maintain a functional heat level within the weapon.  As you might have concluded, a lot of brain power has gone into keeping those guns firing.

•  Machine guns overheat and there are different ways to address the issue. 
• Machine guns are powerful weapons.
• Machine guns fire rapidly and repeatedly.
• None of these

We often let others know what we are thinking without using words. The name that we give for this kind of communication is body language. Body language includes gestures, facial expressions, and posture. Body language does not always mean the same thing to everyone.
Which of the following details would best support the main idea of this passage?

• We sometimes use words to express ourselves.
• Body language may not mean the same thing to everyone.
• Body language includes gestures, facial expression, and posture.
• None of the above

What is the central idea?
 There are many types of lethal venom in the animal kingdom, but perhaps no stranger carrier than the platypus. The platypus is one of few venomous mammals.  Males carry a venom cocktail in their ankle spurs that incapacitates victims with excruciating pain.  Stranger still, the platypus is the only mammal that uses electroreception.  What this means is that the platypus uses its bill to sense the electricity produced by the muscular movements of its prey.  The platypus neither sees, hears, nor smells its prey while hunting but, rather, pursues it through electroreception.  Perhaps most odd, the platypus is the only mammal that lays eggs rather than giving birth to live young.  The platypus is an odd creature indeed.  

• The platypus is an odd, poisonous creature.
• Platypus males have a poison ankle spur.
• Platypus can sense electricity
• None of these options

Many books, papers, and television shows have created an image of the African wild dog as the ultimate predator. According to these sources, the dogs' coordinated teamwork and their unusual endurance help them catch about eighty percent of their prey. A 2012 study tested that notion. Researchers fit a pack of wild dogs with special collars that recorded the dogs' positions and speeds. The data that the collars recorded allowed the researchers to learn what the dogs did when they weren't being observed. The results provided a surprising contrast with the dogs' fierce reputation. The dogs never used teamwork in their hunts; they chased their prey over short distances as opposed to long runs; and instead of eighty percent, they brought down only about sixteen percent of their prey.
Which of the following would be the best title for this passage?

• The History of Wild Dogs
• The Science Behind the African Wild Dog
• African Wild Dogs:  Ultimate Predators?
• African Wild Dogs:  The Undoubted, Ultimate Predator

Read the passage and identify the correct central idea.
Though forks were first used in China thousands of years ago, it took a long time for them to make their way to what is now the United States. 
Ancient Greeks began using forks after the Chinese. However, they did not use forks for eating. They used them for serving food. From Greece, forks moved to the Roman Empire. Romans first used long forks for cooking and serving. By the 300s, they began using table forks to feed themselves. 
The table fork spread from there to what is now the Middle East and Turkey, before arriving in Italy and becoming popular in the 1000s. It stayed popular in southern Europe, but was not used much in northern Europe until it first became popular in France and Spain in the 1700s. 
The table fork arrived in England from France before making its way to the North American colonies, where it first became popular shortly before the American Revolution.

• The fork is a valuable tool that is used in many countries today.
• The fork changed after arriving in the Roman Empire.
• Roman forks were longer than Greek and Chinese forks.
• Forks are superior to other utensils because they have been around longer throughout history.

Most people think that Johann Sebastian Bach played the piano, but this is not true. The piano was not invented until just two years before he died. Bach's main instrument was the organ. He was a great organist. He wrote a lot of wonderful music for that instrument. He also played other keyboard instruments that were ancestors of the piano. Among these instruments was the harpsichord. Along with Mozart, Bach is considered to be one of the all-time great composers
What is the main idea of this paragraph?

• Mozart and Bach did not compose music for the piano.
• Johann Sebastian Bach was a great organist and writer.
• The piano had not been invented three hundred years ago.
• The harpsichord was a keyboard instrument before the piano.

In the Gold Rush of 1849, some one hundred thousand immigrants were lured to California by the promise of gold. Towns and businesses popped up to accommodate the growing population, but a problem remained: how to communicate across the vast reaches of the United States. Three businessmen thought they had an answer: faster mail delivery via the Pony Express, a relay system of horses and riders. The Pony Express made its first delivery on April 14, 1860. Mail from St. Joseph, Missouri, reached San Francisco in just eleven days, rather than a month or more, which was standard for mail delivery at the time. The Pony Express was a short-lived solution, however. After just eighteen months, it was replaced by a national telegraph wire.
Which of the following details would best support the main idea of this passage?

• Many people thought that 11 days was an impossible delivery time.
• From 1866 until 1889, the Pony Express logo was used by stagecoach and freight company Wells Fargo.
• The riders received $100 a month as pay.
• The demand for a faster way to get mail and other communications to and from California became even greater as the Civil War approached.

Read the paragraph and identify the central idea.
Creating Lake-Effect Snow
Buffalo, New York, situated on Lake Erie, one of the Great Lakes, is one of the snowiest cities in the United States. Like other cities on large lakes, it is subject to a phenomenon called lake-effect snow. Water retains heat, so lake water is often warmer than the air. In the lake effect, cold air moves over warmer lake water, initiating a process that can produce large snowstorms. Moisture from the lake evaporates into the cold air, warming it. Because warm air is less dense than cold air, it begins to rise and move away from the lake, cooling down as it does. As the air cools, moisture condenses and forms into clouds. If the temperature is cold enough, the moisture falls to the ground as snow.

• In the lake effect, warm air, which is lighter than cold air, rises and moves away.
• When cold air moves over the warmer water of a lake, lake effect snow can be produced.
• The city of Buffalo, NY receives the most lake effect snow than any other city.
• Large snowstorms are produced by lake effect snow.

What's Beneath Your Plane?
As Shane Loeffler, a geology student at the University of Minnesota, was flying home from Europe, he looked down at the landscape and began to wonder what he was flying over. He realized that a plane flight would be a good opportunity for people to learn about the geological features of the earth below them. As a result of this experience, with a grant from the National Science Foundation, he created a free app called Flyover Country. The app provides users with information on natural formations, man-made features like dams, and even where fossils can be found. The features are pinpointed on a map that corresponds to the landscape below the plane.
Which of the following details would support the central idea?

• The app can be downloaded from iTunes, The Chrome web store, or on Google Play.
• The app pinpoints on a map the landscapes below the plane that a person is flying over.
• Shane Loeffler is a geology student at the University of Minnesota.
• The National Science Foundation provided a grant to Shane Loeffler.

The modern baseball has come a long way from early baseballs. In the 1840s and 1850s, pitchers often made their own balls by hand. One of the most popular balls of the time was known as the "lemon peel" ball. The lemon peel ball was composed of a single piece of leather wrapped around a core with four lines of stitching. Today's Major League baseball must measure between 9 and 9.25 inches and weigh between 5 and 5.25 ounces. However, there were no standards for lemon peel balls, which were generally smaller and lighter than today's balls. While today's official ball must be white and stitched with waxed red thread, the lemon peel ball was often a dark brown leather and had a variety of stitching colors.
What is the central idea of the passage?

• The lemon peel ball was one of the most popular early baseballs.
• In the beginning of baseball, pitchers had to make their own baseball by hand.
• There are strict standards for today's Major League baseball.
• Today's baseball is quite different from early balls, such as the lemon peel.