4. To cut down air pollution, we should take the bus or subway instead of driving. 为了减少空气污染，我们应当乘坐公汽或地铁而不是开车。

　　5. I used to be able to see stars in the sky. 我过去能在天空中看到星星。

　　6. The air has become really polluted around here. I’m getting very worried. 这儿的空气真的已经被污染了，我非常担心。

　　7. No scientific studies have shown that shark fins are good for health. 没有科学研究说明鱼鳍对人们的健康有好处。

　　【考点详解】

　　1. pay的基本用法

　　(1) pay (sb.) money for sth. 付钱(给某人)买……

　　例：I have to pay them 20 pounds for this room each month. 我每个月要付20英磅的房租。

　　(2)pay for sth. 付……的钱。

　　例：I have to pay for the book lost. 我不得不赔丢失的书款。

　　(3)pay for sb. 替某人付钱。

　　例：Don't worry! I'll pay for you. 别担心，我会给你付钱的。

　　(4)pay sb. 付钱给某人。

　　例： They pay us every month. 他们每月给我们报酬。

　　(5)pay money back 还钱。

　　例：May I borrow 12 yuan from you? I'll pay it back next week. 你能借给我12块钱吗?下周还你。

　　(6)pay off one's money 还清钱。