BBU-Rru之间断链可能是由于（）
A.BBU光模块坏
B.光纤断
C.RRU断电
D.RRU坏
参考答案：A, B, C, D
There are few boys in the pool,_______? [ ]
A. are there
B. are not there
C. is it
D. is not it
牵引变电所的电压损失就是（）绕组的电压损失。
