问题补充:
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
答案:
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。