问题
单项选择题
He () his mother a letter at that time.
A．is writing
B．was writing
C．will write
D．has written
答案
参考答案：B
解析：
at that time意为“在那个时候”，用过去进行时。故选B。
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He () his mother a letter at that time.
A．is writing
B．was writing
C．will write
D．has written
参考答案：B
解析：
at that time意为“在那个时候”，用过去进行时。故选B。