A sudden stop can be a very frightening experience ,（）if you are travelling at high speed.

A. eventually

B. strangely

C. merely

D. especially

X线机滤过板的作用是（）。

A.降低皮肤剂量

B.减小骨吸收量

C.滤掉低能X线

D.提高射线能量

E.降低射线能量