Thank you very much and the examples you've are great. Could I ask you another question"What's the distinguish between 'what time' and 'which time'"?

"at what time?" --> We would use this as a question. e.g. At what time did the intruder break into the house? (Sorry, I've been watching a lot of detective movies) " at which time" --> We would use this as a connector to introduce something that happened AT that time. e.g. The break-in happened at 2 am, at which time the suspect was with his friends at a pub. Here, there are 2 clauses : 1. "The break-in happened at 2 am" and 2. "the suspect was with his friends at a pub". AT WHICH TIME is telling us that clause 2 is describing 2 am in clause 1. Hope this helps.

at which 是特殊用法，相当于when at whattime是问具体的时间