问题补充：
Yang Liwei was a student at this flight school from 1983 to 1987, he studied very hard and was made chairman of the Students’ Union.
A. during which time
B. for which time
C. during whose time
D. by that time
答案：
(答案→)A. during which time
B. for which time
C. during whose time
D. by that time
解析：考查定语从句，介词+which的用法，先行词是from 1983 to 1987,，说明是在那段时间，用during，which指from 1983 to 1987，句意是：杨利伟在1983到1987年在这个飞行学校做学生，在这段时间他学习努力，当选学生会的主席。选C。
