问题补充：
Mark was a student at this university from 1999 to , 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：此题考查非限制性定语从句。首先排除D项，因为它构不成定语从句；was made chairman为短暂动作，不能加for引导的一段时间，因此，排除B项；C项关系代词“whose” 应用错误，1999 to 并不为Mark独有。故应选择A项。全句意为:马克从1999年到在上大学，在这几年期间他学习刻苦，被选为学生会主席。
