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
23. My father is getting older and cannot jump as ____ as he could before.
A. high B. higher C. highest D. the highest
24. The Kings have been in Beijing for three years, so they are familiar ____ the city.
A. to B. with C. for D. on
