DF4B型内燃机车硅整流装置每一桥臂上由（）整流元件并联而成。

A、4个

B、6个

C、8个

D、7个

The advantage of geostationary satellites is（）.

A.the range of antenna can cover everywhere in the world

B.we can know the ship’s exact position

C.that the distress alert can be located as soon as possible

D.antenna of permanent earth stations may be directed towards fixed points in the sky