This new form of manufacturing depended on the movement of goods to distant locations and a centralized source of laborers.

^{Before 1815 manufacturing in the United States had been done in homes or shops by skilled artisans. ■A As master craft workers, they imparted the knowledge of their trades to apprentices and journeymen. ■B In addition, women often worked in their homes part-time, making finished articles from raw material supplied by merchant capitalists. ■C After 181 5 this older form of manufacturing began to give way to factories with machinery tended by unskilled or semiskilled laborers. ■D Cheap transportation networks, the rise of cities, and the availability of capital and credit all stimulated the shift to factory production}

The need to circulate air to prevent such a blast could explain why the crew left two hatches open.

^{A possible explanation is that some event made the captain fear for the safety of the ship. ■A In fact, recently studied seismic records indicate that a violent earthquake, whose epicenter was on the seafloor in the region where the Mary Celeste was sailing, occurred some days before the ship’s discovery. ■B If the ship had been subjected to intense shocks caused by the quake, all abroad may have hastily abandoned ship to avoid what they imagined might be its imminent destruction from an explosion of the combustible cargo. ■C A severed rope found dangling from the side of the Mary Celeste suggests that the evacuees trailed behind in the lifeboat, attached to the ship, waiting for the crisis to pass. ■D Great waves may then have snapped the rope and capsized the smaller boat, whose occupants would have disappeared without a trace.}

In contrast, a nearly flawless diamond that is not professionally cut will not acquire its full reflective potential, and thus, its value may be diminished.

^{The final characteristic is cut. ■A When shaped – whether round, oval, emerald, marquise, pear, or heart—the diamond should be faced so that light is directed into the depths of the prism and then reflected outward again. ■B A well-cut diamond will separate the light into different colors when the light is reflected. ■C Only stones of similar shape should have their reflective qualities compared, as some shapes are more reflective than others. The round shape is the most reflective. ■D}

It is the only method available for obtaining a variety of colors in bamboo.

^{For centuries, bamboo has provided building materials for Eastern cultures. Now it is becoming more popular and available in the West, particularly as a substitute for expensive hardwood flooring.} ■^{A As a flooring material, natural honey-colored bamboo is more stable than carbonized bamboo.} ■^{B Carbonizing is a technique of steaming and pressurizing the bamboo to introduce carbon fibers that darken the original material.} ■^{C However, it lowers the hardness factor, making the darker bamboo more susceptible to damage.} ■^D

The ear is generally divided into three main sections: the outer ear, the middle ear, and the inner ear.

^{■A Of all the organs that help maintain equilibrioception, perhaps the most important is the ear. ■B To understand how the ear helps us maintain our sense of balance, it is useful to examine the ear’s anatomy. ■c The outer ear primarily assists the hearing, or auditory, system. ■D It acts as a type of preamplifier by collecting sounds from athe environment and funneling them to the eardrum.}

In fact, damage to the environment by humans is often much more severe than damage by natural events and processes.

■A Ecologists are especially interested to know what factors contribute to the resilience of communities because climax communities all over the world are being severely damaged or destroyed by human activities. ■B The destruction caused by the volcanic explosion of Mount St. Helens, in the northwestern United States, for example, pales in comparison to the destruction caused by humans. ■C We need to know what aspects of a community are most important to the community’s resistance to destruction, as well as its recovery. ■D

Unless something acts to halt this migration, these natural resources will eventually reach the surface.

Continued sedimentation—the process of deposits’ settling on the sea bottom—buries the organic matter and subjects it to higher temperatures and pressures, which convert the organic matter to oil and gas. ■A As muddy sediments are pressed together, the gas and small droplets of oil may be squeezed out of the mud and may move into sandy layers nearby. ■B Over long periods of time (millions of years), accumulations of gas and oil can collect in the sandy layers. ■C Both oil and gas are less dense than water, so they generally tend to rise upward through water-saturated rock and sediment. ■D

This, however, was not the case.

^{Experiments have also cast serious doubt on the belief that yawning is triggered by a drop in blood oxygen or a rise in blood carbon dioxide. ■A Volunteers were told to think about yawning while they breathed either normal air, pure oxygen, or an air mixture with an above-normal level of carbon dioxide. ■B If the theory was correct, breathing air with extra carbon dioxide should have triggered yawning, while breathing pure oxygen should have suppressed yawning. ■C In fact, neither condition made any difference to the frequency of yawning, which remained constant at about 24 yawns per hour. ■D Another experiment demonstrated that physical exercise, which was sufficiently vigorous to double the rate of breathing, had no effect on the frequency of yawning Again the implication is that yawning has little or nothing to do with oxygen.}

This spaciousness also makes the gambrel roof highly suitable for barn construction, since the upper floor can be used as a hayloft.

^{The gambrel roof design has an enduring appeal to many builders and homeowners. Originally a feature of Dutch colonial architectural style, the gambrel is a straight double-sloped roof joined at a central ridge. ■A The main distinguishing feature is that each roof side is broken into two planes, with the lower slope inclined at a steeper pitch than the upper. Sometimes the angle of the gambrel roof becomes shallower again at the eaves and projects over the wall of the house, giving a bell-shaped appearance in cross section. ■B The main advantage of the gambrel roof is that it creates a spacious interior on the upper floor of the house. ■C This makes it a perfect choice for a growing family. ■D}