4. As we all know,the moon is a s of the earth.

3. Anything that is dropped falls towards the centre of the earth because of the pull of g .

2. A p is a scientist who has special knowledge and training in physics.

1 . A b is a scientist who studies biology.

6. She studied hard;(因此她获得面分) 

5. The couple brought up their children on low incomes. Now the children, (轮到他们) ，should look after their elder parents.

4. Do you believe (火星上有生命) ？

3. Luckily,the doctor (及时前来挽救了他的生命) .

2. What can we do to (防止这种疾病蔓延) ？

1. She (生了一个健康的婴儿) last night.