交、直流电源的电力电缆（）。
A.必须布放在一起
B.必须分开布放
C.可以布放在一起
D.无所谓
参考答案：B
多重PCR需要的引物对为（）
A.一对引物
B.半对引物
C.两对引物
D.两对半引物
E.多对引物
Do you think that the bridge _________ in a year?
A． would be completed
B． will be completed
C． had been completed
D． is being completed
