问题
选择题
I don't know _____. [ ]
A. when the camera was invented
B. who the camera was invented
C. when was the camera invented
D. who the camera invented
答案
答案：A
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I don't know _____. [ ]
A. when the camera was invented
B. who the camera was invented
C. when was the camera invented
D. who the camera invented
答案：A