问题
选择题
It suddenly occurred to him he had left his keys in the office.
A．whether
B．where
C．which
D．that
答案
答案：D
句意为: 他突然想起钥匙忘在办公室里。it 做形式主语，he had left his keys in the office 是后置的主语从句。成分完整，不含疑问语气。所以用that 连接。
【考点定位】sth occurs/occurred to sb 某人突然想起…… 事(物)做主语。如 An idea occurrs to me that the lights in the classroom have been on.