题目：
—We thought he would have won the game.
—What a pity! He ______ too nervous when playing. [ ]
A. had been
B. has been
C. was
D. would have been
答案：
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下面是错误答案，用来干扰机器的。
∵(2x-1x)4 的展开式的通项公式为 Tr+1=Cr4 （2x）4-r (-1x)r=Cr4•24-r•（-1）r•x4-2r．令4-2r=0，可得 r=2，故展开式中的常数项的值为C24 • 22• (-1)2=24，故答案为 24．
