There _____________ a library in our school. [ ]
A. is
B. are
C. be
答案:A
已知抛物线C:y2=2px (p>0)上一点P(6,m)到其焦点F的距离为7,则抛物线C的以点M(2,1)为中点的弦AB所在直线的方程为______.
水压试验时,为什么要缓慢升压