is moved
since的搭配有四种
1.since +过去一个时间点 (如具体的年、月、日期、钟点、1980,last month,half past six).
I have been here since 1989.
2.since +一段时间+ ago
I have been here since five months ago.
3.since +从句
Great changes have taken place since you left.
4.It is +一段时间+ since从句
It is two years since I became a postgraduate student.
这里应为从句一般过去时,代表过去一个时间点