变压器系_________、________跳闸，在未查明原因和消除故障之前，不得送电
参考答案：瓦斯，差动保护动作
He has worked in the city _______ three years ago while his wife has been here______only one month.
A．since , for
B．since, since
C．for, since
D．for, since
目前，我国通过证券交易所进行的证券交易均采用( )方式。
A．书面报价 B．电脑报价 C．口头报价 D．传真报价
