根据句意和首字母提示，写出各句中所缺单词的正确形式。

1. —It is so clean!

    —We s________ the floor just half an hour ago.

2. The boy h________ eating rice day after day.

3. Some t________ like surfing the Internet very much.

4. Karen b________ a storybook from one of her friends.

5. Good s________ should not have too much fat or sugar.

同一巡航高度层的航空器在交叉航迹上飞行，同时使用位于航迹交叉点的测距台测距时，航空器之间的最低间隔为（）千米。

A.40

B.30

C.60

D.70