The thief broke in, trying to open the safe but ________.
A.in no wayB.in vainC.without effectD.at a loss在线课程B
解析：
句意：小偷闯了进来，试图打开保险柜，但徒劳无功。in no way绝不。如：In no way should the result be seen as a defeat for the government.这种结果绝不能被视为政府的失败。in vain--uselessly; without a successful result 白费地，徒劳无益地。如：They tried in vain to make him change his idea.他们想让他改变主意，却白费心机。at a loss--uncertain what to do, think or say; confused困惑，（茫然）不知所措。如：I was at a loss for words when he told me the news.当他告诉我那个消息时，我不知说什么好。