An average of 130,000 Chinese       aboard for studies every year over the past few years, improving

exchanges in the educational fields. [ ]

A. was going      

B. have been going    

C. has been going    

D. are going

充气消防车的过滤系统相连接监视过滤状况，当数字LCD屏显上显示快速参考色为红色时表示（）。

A.滤芯可继续使用

B.滤芯即将需要更换

C.表示滤芯必须更换

D.监视器故障