2019年小升初英語(yǔ)閱讀理解天天練（九十八）

　　（九十八）

　　There is another aspect of flying we must now know about, that is flying speeds. There are, in fact, tow kinds of speed: the ground speed, which is the actual speed of the plane in relation to the ground, and the air speed, which is the speed relative to the air. These are two quite different things.

　　Let us go back to the kite for a moment. If, in still air, you run with a kite at five miles per hour, its ground speed will be five miles per hour because that is the actual speed at which you are pulling it over the ground. Now, suppose you are running at five miles per hour. The ground speed will still be the same but, because the air is passing the kite at ten miles per hour, the air speed of the kite will be ten miles per hour; that is , the speed at which you are running plus the speed of the air blowing past the kite. Stand still with your kite in the same breeze. Its ground speed is now nothing, but the air is passing the kite at five miles per hour, so its air seed is five miles per hour.

　　Ground speed decides how long an plane will take to fly from one place to another. Air speed provides the lifting force and the drag. Your kite will remain in the air in a good breeze even if you stand still, and you will still feel the drag on the string.

　　36. In fact, there are two kinds of speed:

　　one is the ground speed, the other is ____.

　　A. flying speed                      B. full speed

　　C. air speed                         D. first speed

　　37. What's the ground speed if you run with a kite at five miles per hour in still air.

　　A. It will be five kilometers per hour.

　　B. It will be more than five kilometers per hour.

　　C. It will be five miles per hour.

　　D. It will be five feet per hour.

　　38. According to the passage, what is the running speed plus the air speed of the kite?

　　A. Ten miles an hour                   B. Five miles an hour

　　C. At least five meters.                 D. More than ten miles

　　39. Air speed provides _____ and drag.

　　A. motive force                        B. wind force

　　C. lifting force                         D. constant force

　　40. How many different things does the writer talk about.

　　A. Three.         B. Two.        C. One.        D. Four.