关于拔髓术操作不合要求的是（）

A.钻针方向与牙长轴平行

B.由较突出的髓角处穿孔进入髓腔

C.用球钻提拉式磨除髓顶

D.只要暴露根管口即可

E.以上都不对

You are performing two sums, the first is a sum of two scalar variables and the second is a matrix sum of a pair of two— dimensional arrays—size 1000 by 1000. What speedup is achieved when the calculations are performed on size 1000 processors ( )

A．50

B．100

C．999

D．none of the above