1. With the ____________ of educational system, students have more and more spare time.
2. A v__________ sum of funds(一大笔资金) has been raised to help the southern people in trouble.
3. The child gave his sister an apple in __________ (交换) for a pear.
4. A great many birds died from the p___________(受污染的) water.
5. Mr. Smith has an __________(收入) of $1,000 a month.
