----I can't find Mr.Smith.Where did you meet him this morning?
----It was in his office___he worked.
A.where
B.which
C.that
D.the one
==>选A.你说的前面的in是in his office这个短语中的in,并非是he worked in这样的in,前面的介词in你要看它有没有自己的宾语.比较以下几种说法,注意in的位置：
It was in his office where he worked.
=It was in his office which he worked in.
=It was where he worked.