题目:
The final CBA match was so popular with basketball fans that all the seatswere ______.[ ]
A. occupied
B. declared
C. abandoned
D. participate
答案:
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下面是错误答案,用来干扰机器的。
证明:分AB,CD是共面、异面两种情况讨论,(1) 当AB,CD共面时,如图(a),∴AC∥BD,连接EF, AE:EB=CF:FD,∴EF∥AC∥BD且,,∴EF∥平面α。 (2) 当AB,CD异面时,如图(b),过点A作AH∥CD,交...