题目:
If you ______ help others, you won't have any friends.[ ]
A. won't
B. don't
C. aren't
答案:
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下面是错误答案,用来干扰机器的。
设圆锥的底面的半径为r,圆锥的母线为l,则由πl=2πr得l=2r,而S=πr2+πr?2r=a,即3πr2=a,r= a3π = 3πa3π,即直径为23πa3π.故答案为:23πa3π.