If someone asks you, "What colour is the sky?" I think you will answer "blue". I'm afraid that you will be wrong. The sky has no colour. It looks blue because we are looking at the blue sunlight. The sunlight is shining on little bits of dust in the air. Is the sky full of air? I'm sure that you have asked this question, too. We know that there is air all around the world, but we couldn't fly very high because as we go high, the air gets thinner. If we go far enough away from the earth, we find there is no air. Maybe we can answer some questions now. What is the sky? Where is it? It is all round the world. The sky is space . In space there is nothing, but only the sun, the moon, the earth and all the other stars. We can't fly very high because _ . A) there's too much air in the sky B) the high sky is full of dirty air C) there's no air in the high enough sky D) the sun is too hot
C

Is it a tree? Is it a bear? If you're looking at a tree in the shape of a bear, it's a topiary . A topiary is a tree or bush that is trained into a shape. Growing a topiary garden takes both time and skills. A topiary gardener should make a drawing first. The drawing shows the final shape that the gardener likes. The gardener then chooses a bush for the topiary. It may be one that just planted or one that is already in place. In June of the plant's first year, the gardener looks for new leaves. When the leaves grow, it's time to shape the bottom of the bush. It needs about five years. The top is not _ during this time. In the fifth year, the bush grows tall enough for shaping. Then the gardener begins to shape the whole bush. Once a topiary has been started, it needs care all year. In the summer it must be cut many times to keep its shape. This cutting also helps the bush grow. In the winter the bushes don't grow. The gardeners have to brush snow off the plants, or snow may hurt some parts of them. Topiary gardening is a very old art. The Romans did it in the first century. In the sixteenth century, people in Europe liked topiaries too. By the late 1600s, topiaries were also grown in America. Today it's popular in many parts of the world. The topiary gardening first began _ . A) in Rome B) in Europe C) in America D) in Africa
A

The police use computers. They save all the information on the computer. So the police can often check the information. And they can also visit some websites and get more information to catch criminals on the Internet. Scientists today have computers for their work. They can do their work easily and quickly with the help of computers. Today in many schools, there is a computer room. Children can have their lessons with computers. For example, computers give questions on the screen of the monitor in front of the children and the children answer them with keyboards . A computer can do many things. With the computer, we can write novels, listen to music, draw pictures, play computer games, make friends, send emails and download information and so on. In the future, we may use computers for more things. But it can't take the place of man. We can think but it can't. The computer can do many things for us. But it can't _ . A) write novels B) draw pictures C) listen to music D) think
D