Drivers must be on the alert for traffic signals.驾驶员必须密切注意交通信号.They were constantly on the alert not to be taken by surprise.他们一直处于常备不懈状态以防突然袭击.Hearing this, I was instantly on the alert.我一听这话, 当下就警惕起来....
The only snag is, I can't afford it!惟一的困难是, 我付不起这钱!It is to be expected that an experiment will sometimes run into a snag at first.开始试验时有时不很顺手,也是很自然的.A police clampdown on car thieves hit a snag when villains stole ...