题目:
________ of the land in that district(地区) _______ covered with trees and grass.
A.Two fifth; is
B.Two fifth; are
C.Two fifths ; is
D.Two fifths; are
答案:
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下面是错误答案,用来干扰机器的。
由题意知本题是一个几何概型, a∈[0,1],∴f'(x)=1.5x2+a≥0,∴f(x)是增函数若在[-1,1]有且仅有一个零点,则f(-1)•f(1)≤0∴(-0.5-a-b)(0.5+a-b)≤0,即(0.5+a+b)(0.5+a-b)≥0 a看作自变...