问题
选择题
John said he _______ the movie yesterday. [ ]
A. watch
B. watches
C. watched
D. to watch
答案
答案：C
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John said he _______ the movie yesterday. [ ]
A. watch
B. watches
C. watched
D. to watch
答案：C
，BC边长为2L，该介质的折射率为
。求：
或
）。