问题
选择题
We are going camping _________ 6:30 _________ the morning of December 22nd. [ ]
A. in; on
B. on; at
C. at; on
答案
答案：C
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We are going camping _________ 6:30 _________ the morning of December 22nd. [ ]
A. in; on
B. on; at
C. at; on
答案：C
且B=P-1AP，
时，求矩阵B；