问题补充：
The clever boy made a hole in the wall, he could see what was going on inside the building.
A. on which
B. at which
C. through which
D. in which
答案：
A. on which
B. at which
(答案→)C. through which
D. in which
解析：这题考查定语从句：介词+which，句意是：聪明的男孩在墙上打了个洞，通过这个 洞他可以看到大楼里发生的事。选C。
