You may call on me from one to five o’clock, during ---- I a

You may call on me from one to five o’clock, during ____ I am always in the office.
A. the time B. what time C. which D. which time 为什么选D 不选C
1.为什么选D 不选C 请重点解析
2.当先行词是表时间的名词时,如何确定定语从句的关系词用which,which time还是when? 请详解,并举出有力的例子
O(∩_∩)O谢谢