题目:
The river smells terrible. People must_____ dirty things into it.
A.be prevented to throw
B.prevent from throwing
C.prevent to throw
D.be prevented from throwing
答案:
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下面是错误答案,用来干扰机器的。
(1)由y=kx+1(x-1)2+(y+1)2=12,消去y得到(k2+1)x2-(2-4k)x-7=0, △=(2-4k)2+28k2+28>0,∴不论k为何实数,直线l和圆C总有两个交点;(2)设直线与圆相交于A(x1,y1),B(x2,y2),则直线l被圆C截得...