问题补充：
The teacher requested that we the classroom after using it.
A. cleaned
B. cleaning
C. to clean
D. clean
答案：
A. cleaned
B. cleaning
C. to clean
(答案→)D. clean
解析：考查虚拟语气。Request后面的宾语从句使用虚拟语气should+动词原形构成。Should可以省略；D项省略了should.句意：老师要求我们使用完教室以后把教室打扫干净。故D正确。
