.they were singing, the teacher came in. A. BeforeB. afterC. AsD. Until

发布时间：2020-08-17 15:01:46

.    they were singing, the teacher came in.
A. Before
B. after
C. As
D. Until

网友回答

A. Before
B. after
(答案→)C. As
D. Until
解析：表示正当什么时候，用as
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