问题补充：
What you when you father came back?
A. did, do
B. are, doing
C. were, doing
D. do, do
答案：
A. did, do
B. are, doing
(答案→)C. were, doing
D. do, do
解析： 考查固定结构。Be doing…when…某人正在做某事。。。这时。。。；根据when you father came back指的是过去，所以用过去进行时，选C。
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