国家开放大学 / 综合英语（2）
正确率：100%
The students _ _ _ _ _ _ at their desks when Mr. Black _ _ _ _ _ _ .
a.waited, arrived
b.were waiting, were arrived
c.were waiting, arrived
d. waited, were arrived
a.waited, arrived
b.were waiting, were arrived
c.were waiting, arrived
d. waited, were arrived
参考答案：
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