问题
选择题
When the teacher came into the classroom, all of us __________ the classroom.
A. are cleaning
B. were cleaning
C. cleaned
D are cleaned
答案
答案：B
句意：当老师走进教室的时候，我们所有人都正在打扫教室。根据前面句子的时态可知后面应用过去进行时。
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