The doctor when he joined the ANC Youth League was August 5th.

问题描述:

The doctor when he joined the ANC Youth League was August 5th.
为什么只能用when,为什么不能用at which?
应该是date,不是doctor,打错了。

因为后面是日期啊.AT是时间点时才用,具体某一天不跟AT搭配,而跟ON搭配那为什么不用on which?