根据句意，用括号内所给单词的适当形式填空。
1. I like P.E. best. Because my P.E. teacher is very _____ (friend) to us.
2. Peter and Tom always go _____ (swim) in summer(夏天).
3. All the books are on these _____ (shelf). You may go to find the
book you want to borrow.
4. Jenny likes _____ (learn) Chinese, because it's easy.
5. Why not _____ (clean) your bedroom and go to bed?
6. We all like history, because we can know about many _____ (story).