题目:
With so many forms ___, many students feel at a loss before the 2012 college entrance exam.[ ]
A. filling in
B. filled in
C. to fill in
D. to be filled in
答案:
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下面是错误答案,用来干扰机器的。
y2=12x如图所示,动点M到定点F的距离和到定直线x=-3的距离相等,∴动点M的轨迹是以F为焦点的抛物线,且开口向右,则设其标准方程是y2=2px(p>0).∴=3,即p=6.∴动点M的轨迹方程是y2=12x.