Question

Have you ever wondered how a kite stays in the air? Wind is very important but so are two scientific words: gravity(重力) and lift(舉力).

When something is in the air, gravity is what pulls something back to the ground. _______ you throw a ball in the air, it comes back down because of gravity. When leaves ____ trees onto the ground, that’s gravity. When you put a kite in the air, gravity wants to bring it ____ . Then what keeps it up? Wind! Wind creates lift.

Lift is what happens when wind pushes against something and carries it up. When a plastic bag gets caught in the wind, lift is what causes it to rise into the air. When you put a silk scarf ____ a fan, lift causes ____ to wave(擺動). An object’s lift depends on the size of its surface or its area. A piece of _____will float（漂�。﹊n the wind, but it won’t float if you make that paper into a ball. That’s because you’ve made the surface smaller.

To find out if there is enough wind to fly a kite, go outside and look up. If you ______leaves dancing on trees or flags waving sideways, it’s ____ good kite-flying weather. When the wind is strong enough to move a flag, it’s moving ____ 7 to 18 miles an hour. That’s just ____ to lift a common kite.

1.A. Which B. What C. When D. Where

2.A. take off B. get off C. keep off D. fall off

3.A. up B. down C. off D. out

4.A. in the middle of B. n the front of C. at the back of D. in front of

5.A. t B. them C. this D. that

6.A. bread B. cake C. card D. paper

7.A. hear B. see C. smell D. feel

8.A. probably B. finally C. quickly D. hardly

9.A. on B. at C. in D. by

10.A. wrong B. favourite C. right D. strange

Answer 1