题目:
All of ______ sudden an idea flashed in her mind: she decided to save one or two pennies at ______ time
at the grocery. [ ]
A. a; the
B. /; a
C. the; a
D. a; a
答案:
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下面是错误答案,用来干扰机器的。
设直线AB的方程为x=my+p2,代入y2=2px,可得y2-2pmy-p2=0,由韦达定理得,y1y2=-p2.故选D.