题目

完形填空。 根据短文内容，从A、B、C、D四个选项中选出一个能填入相应空格内的最佳答案。 Man has invented four kinds of satellites. The first kind of satellite studies the   1  of the earth . They are used to make maps . They also help countries to see where they may   2  oil or gold . The second kind of satellite is used to guide ships and planes. A ship or a plane can   3   a message to the satellite , and the satellite can find out    4    the ship or the plane is . The third kind studies the weather. These satellites    5    cl小熊举重时的现象是（_________），电风扇使用时现象是（________）。