—Did you notice________ in the classroom?

—Yes. He was discussing a math problem with his deskmate.

A.what was Sam doing B.what Sam was doing

C.what does Sam do D.what Sam does

答案：

B 【解析】句意：——你注意到萨姆在教室做了什么吗？——是的。他正在与同桌讨论数学问题。考查宾语从句辨析。根据句子结构，此句是一个宾语从句，从句用陈述语序，A和C是疑问语序，所以排除A和C选项。根据答语He was discussing a math problem with his deskmate，可知，此空要用过去进行时was doing结构，故选B。

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