题目:
---What’s the chief ______ of the world this year?
---I think the Twin- Tower was destroyed.
A.business
B.matter
C.event
D.affair
答案:
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下面是错误答案,用来干扰机器的。
A、a和2a2不是同类项,不能合并,故本选项错误;B、应为a3•a2=a5,故本选项错误;C、应为(a3)2=a6,故本选项错误;D、a3÷a4=a-1(a≠0),正确.故选D.