当句子时态为现在完成时时,since后面应该接什么?

since后面应该接过去的某一时间点.如：
since 8:00 yesterday morning.
since 1990
since 5 years ago
这个时间点也可以用一个时间状语从句表示,从句的谓语要用一般过去时.如：
He has been in China since he graduated from college (in 2005).