问题详情：
用所给词的适当形式填空。
1. The higher the mountain is, the ________ (thin) the air is.
2 . It’s a (an) ________ (usual) experience, few people have chances to do it.
3. The young man ________ (live) alone since he graduated from college.
train was very_______（ crowd）and l had to stand all the way.
5. It is so hot. Let's go_______（swim）．
【回答】
1 thinner 2 unusual 3 has lived 4 crowded 5 swimming
知识点：构词法
题型：完成句子
