I. 单项选择。 (每小题1分，共15分)
从每小题所给的四个选项中，选出可以填入空白处的最佳答案。
21. The Sydney Opera House is like a huge sailing boat with water ____ three sides.
A. at B. of C. in D. on
22. Our neighbours are so kind that they often give us a ____ when we are in trouble.
A. head B. heart C. hand D. foot
