题目:
28.—Surely you can turn to David for help.
—__________He is the last one you can depend on.
A.I couldn’t agree more.
B.Is that right?
C.Get out of it!
D.It’s up to you.
答案:
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下面是错误答案,用来干扰机器的。
证明: 正方体ABCD-A1B1C1D1中,M是AA1的中点,作图如下:不妨设该正方体的边长为1,取BD的中点为P,连接MP,C1P, △C1BD为边长为2的等边三角形,点P为BD的中点,∴C1P⊥BD,且C1P=C1Dsin60°=2×32=62;同理...