一道英语完形填空题：My exams are over, and so are my student’s exams. She is the first stude

这个空前面用的是现在完成时 I have taught,通常现在完成时是和since配套用的,而before一般用于过去完成时

表示某情况自过去某时间点或某个事件以来一直持续到现在 自…以后，从…以来You use since when you are mentioning a time or event in the past and indicating that a situation has continued from then until now.

表示过去某事或某情况发生后不久又发生了另一件事 此后，后来When you are talking about an event or situation in the past, you use since to indicate that another event happened at some point later in time

她是我上大学以来以来教的第一个学生。have taught是现在完成时，与since（自......以来）搭配。例如， I have been there for three years since he left. 自他离开后，我到那里已有三年了。

自从....以来 现在完成时