Mark was a student at this university from 1999 to 2003, , 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
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(答案→)A. during which time
B. for which time
C. during whose time
D. by that time
解析：1997到2003为一阶段时间，所以用“during which time”引导定语从句，表示“在此期间”。