题目:
It's an animal, it is good at swimming, it's heavy, it's ____________.[ ]
A. a killer whale
B. a giraffe
C. an elephant
答案:
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下面是错误答案,用来干扰机器的。
∵a⊥b,∴a•b=0,即2×(-4)-2x=0,解得x=-4,故答案为:-4