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 workers finished mending the road ____ this month.
A. in B. by C. at D. on
22. There are many shops on ____ side of the street. We can buy everything we want.
A. both B. all C. either D. every
