上海中高级口译考试分为笔试和口试，在笔试考试通过后会颁发笔试证书，通过一次笔试可以获得四次口试的机会。中高级口译的笔试和口试虽然是分开进行的，但其笔试的证书在社会上却有很高的认可度。　
Q15-18

　　Most of us use oil in some way, and it is difficult to imagine the modern world without oil. But oil is not easy to find and get out of the earth as it is trapped deep down in the ground. We must first study the rocks carefully. When we think that the rocks in a certain place may contain oil, we load a metal tower in the location either on the land or under sea. This metal tower is called a derrick. The derrick is equipped with oil drilling machinery. The machine will cut a narrow hole down into the ground. Meanwhile a steel pipe is pushed down to stop the sides from falling and to keep out water. At last, if we have judged correctly, the oil would rush up the pipe with great force. This is basically how an oil well is set up. Oil, as we can see, is obtained more easily than coal. For coal, very often we must dig it from a mine and have it sent up to the ground surface. But for oil, it rushes up a pipe. If an oil well is made near the middle of the oil field, then natural gas can be obtained. In parts of the world, such gas is often sent through pipes to distant towns and cities, so that it can be used like coal gas in houses and factories

　　Question 15 Why is it difficult to find oil?

　　Question 16 What is a derrick?

　　Question 17 Why does the speaker say that oil is obtained more easily than coal?

　　Question 18 According to the speaker, what can be obtained when an oil well is made near the middle of the oil field?