the doors were closed and that all the lights were off, the boy left the classroom.
A. Check
B. To check
C. Checked
D. Having checked
网友回答
A. Check
B. To check
C. Checked
(答案→)D. Having checked
解析：考查非谓语动词。the boy和check是主谓关系，故用主动；check和leave有先后关系，应该用完成时。故选D。