(1) Radiation has serious harmful effects.(2) The major health risk that it poses is an increased risk of developing cancer. (3) Therefore, time spent near an identified source of radiation has been limited. (4) Other harmful effects that have been observed include genetic abnormalities in the children of parents who had significant exposure to radiation. (5) Mental retardation, in particular, has been observed in children whose mother was exposed to a significant amount of radiation.

(1) Carbon monoxide is a colourless gas that turns into carbon dioxide when burned. (2) Produced by burning fuels, carbon monoxide cripples the flow of oxygen to cells and tissues. (3) As a result, they can not function properly. (4) People who suffer from respiratory or circulatory problems are especially vulnerable to health problems from exposure to carbon monoxide. (5) A volatile organic compound is an airborne chemical that contains carbon.

(1) Leadership is solving problems. (2) The day soldiers stop bringing you their problems is the day you have stopped leading them. (3)They have either lost confidence that you can help or concluded you do not care(4) Getting into the habit of working independently requires less effort than collaborating with one's peers. (5) Either case is a failure of leadership.

(1) Water is a chemical substance composed of hydrogen and oxygen and is vital for all known forms of life. (2) Contaminated water can cause many types of diseases, including cholera, typhoid and dysentery. (3) In typical usage, water refers only its liquid form of state. (4) But the substance also has a solid state, ice and a gaseous state, water vapour or steam. (5) On Earth, it is found mostly in oceans and other large bodies of water.

(1) The Earth is becoming warmer.(2) The average temperature has risen by more than 0.5 C in the past century. (3) Thus, wet climates are found on the upwind side of a mountain range, while arid climates are on the downwind side(4) It is predicted to rise by 3 C by 2050, although this figure is far from certain.(5) The effects may be felt by more frequent droughts, violent storms and changing climates.

(1) Birds are warm-blooded, vertebrate animals with four limbs, the front two of which are adapted into wings. (2) They are the only animals that have feathers. (3) They have light, hollow bones and a toothless beak.(4) Therefore, some species migrate to warmer climates during the winter.(5) They lay hard-shelled eggs and most species protect their young until they leave the nest.

(1) Fossils are remains of once-living things preserved in rock. (2) This sequence of illustrations shows how a dinosaur that perished many millios of years ago came to be preserved as a fossil.(3) Most living things are eaten or die and their soft parts rot away leaving no trace. (4) But sometimes hard body parts remain, like the shells, bones, teeth, horns and claws of animals and the bark, cones and seeds of plants.(5) These are the parts most likely to form fossils.

(1) Weather plays an important part in our lives.(2) For example, without rain, our crops would die, but too much rain can cause floods and destroy the crops. (3) Therefore, it is very useful to be able to predict what the weather has in store for us. (4) Weather is the conditions and changes that takes place in the lower atmosphere, up to about twenty kilometres high. (5) To do this, weather forecasters gather information about weather conditions from satellites in space and weather stations.

(1) The plains beneath the Pacific Ocean cover about the same area as all the Earth's land put together. (2) The ocean floor is mostly a level plain.(3) It also features mountain ranges, volcanic peaks, long ridges, deep trenches and high ledges where it borders the continents. (4) This plain lies at an average depth about 4500 metres. (5) Most of its covered by a thick layer of sediment called ooze, the remains of dead organisms that have sunk to the bottom.

(1) The Takla Mahan Desert , China may be a scorching 40 C by day yet plunges to -40 C at night. (2) A desert is an area with very low rainfall, usually with less than 35 centimetres of rain or snow a year. (3) Other than at oases, places where underground eater comes to the surface, there are few signs of life. (4) Deserts may be hot all year round in the Sahara of Africa. (5) Or they may always be cold as in Greenland or Antarctica.

(1) The body's main working parts , such as the brain, heart, lungs and stomach are called organs. (2) Like all the body's organs, they are formed from various types of tissue. (3) The heart never stops beating, pumping blood, which carries nutrients and oxygen to all parts of your body.(4) All the tissues in the human body are themselves made up from tiny building blocks, called cells. (5) There are trillions of cells in the body.

(1) The coast is a continuing battle between sea and land. (2) Waves build up higher in the direction of the prevailing winds in the region.(3) Sometimes the sea loses as sand or mud piles up and the land grows.( 4) In other places, the sea wins as waves batter and break up the coast. (5) Even hard rocks like granite are gradually worn away, especially during storms when high winds whip up huge waves powerful enough to smash pebbles and boulders against the shore.

(1) The planets orbit the sun in the same anticlockwise direction and in oval rather than perfectly circular paths. (2) Seven of the planets and most of their moons, all travel roughly on the same plane. (3) Mercury is the exception. (4) The Kuiper Belt is a region of the solar system lying beyond Neptune, consisting mainly of fragments of frozen methane, ammonia and water. (5) This is because it has a slightly tilted orbit.

(1) A glacier is a moving mass of ice.(2) Glaciers occur in very cold regions, high in mountains and in the far north and south polar regions. (3) Some glaciers snake down mountain valleys. (4) Over many years, the snow piles up at the head of a high valley and compacts into ice. (5) Others such as the ice sheets of Greenland or Antarctica are so huge and thick they almost totally cover the land.

(1) Five billion years from now, the Earth's oceans and atmosphere will disappear. (2) Its rocky surface melt in temperatures of 1500 C.(3) The survival of humanity, as we currently know it, will be tested. (4) The sun will eventually shed its outer layers into space. (5) All that will remain of the sun itself will be, at first, a small extremely dense star before it eventually cools and wastes as a black dwarf.

(1) Constantly streaming away from the sun in all directions are electrically charged particles that make up the solar wind. (2) Travelling at an average speed of about 400 km/sec, they produce magnetic fields and electiric currents across a vast bubble called the heliosphere. (3) The edge of the heliosphere lies up to eighteen billion kilometres from the sun.(4) Some are made of water, ammonia and methane ice.(5) It marks the boundary of the solar system.

(1) The Vikings lived in Scandinavia, the northern part of Europe. (2) They conquered and raided parts of England, France and Germany, and even got as far south as Spain and Italy. (3) Viking ships explored Iceland and Greenland. (4) The Viking Age began at a time when the population of Scandinavia started to grow. (5) They even reached America at about 1000 but the town they founded in North America didn't last very long.

(1) After Vasco de Gama's voyage to India by sea, Portugal began to establish colonies there.(2) Then they opened up trade with Southeast Asia, the Spice Islands, China and Japan. (3) They controlled the sea route from Lisbon to India for most of the 16 th century. (4) Their dominance ,in trade in these areas brought great wealth and power to Portugal. (5) Another fatal mistake they made was to try to convert the natives to Christianity.

(1) There are about 5500 different species of mammals.(2) They range in size from tiny shrews, only a few centimetres long, to the 30 metre blue whale. (3) Marsupials give birth to their young that have not yet fully developed and the young continue to develop while clinging to their mother's body. (4) Most mammals have four limbs and a covering of hair or fur. (5) Sea mammals have adapted to life in the water by losing their hair and forming their hind limbs into a tail.