【正确答案】 C

【答案解析】[听力原文]
Gravity holds us close to the Earth"s surface. Nobody can jump more than a few feet into the air without the force of gravity pulling him down. It takes a powerful engine to keep a plane up in the air. If you throw a ball upwards as hard as you can, you will notice that it travels in a curved path before it comes back to the ground. If the Earth had no gravity, the ball, instead of travelling in a curve, would move away in a straight line; in fact, it would never come back to the ground. If the Earth were to lose its pull of gravity, we should all fly off it as it spins round in space. The Earth has a strong pull, but modern rockets going out into space are able to escape from the gravity, because they travel so quickly. With the ball thrown into the air, the height reached by the ball depends upon how hard it is thrown. The greater the starting-speed, the higher the ball will go. If it could be thrown so that it travelled fast enough, the ball would escape into space and never come back. Nobody can throw a ball as fast as this, but powerful rocket engines can send spaceships away from the Earth at such a speed that the Earth"s gravity is not able to pull them back. This is how we can now send rockets to the Moon.

What can human do?

【正确答案】 A

【答案解析】[听力原文]
How will a flying bail travel without gravity?

【正确答案】 B

【答案解析】[听力原文]
Why the ball someone throws away always ends up turning back to the ground?

【正确答案】 B

【答案解析】[听力原文]
When can spaceships be sent away from the Earth?