【词组解析】

1. on duty 上班,值班

（1）He's on duty twenty-four seven.

       他不分昼夜地天天上班。

（2）The nurse on duty was fearful that the patient should get worse.

       值班的护士担心病人的病情会恶化。

2. on earth 究竟,到底

（1）What on earth is the matter there?

       那里究竟发生了什么事情?

（2）Everything is all right. What on earth are you crying for?

       好好儿的，你哭哪门子？

3. on fire 起火着火；非常激动

（1）Some sparks from a passing train set the haystack on fire.

        一列过往火车迸发出的一些火花点着了干草堆。

（2）She is a person who would set the world on fire.

       她是那种会做出惊人之举引起轰动的人。

4. on foot 步行

（1）The city is best explored on foot.

       最好是徒步考察这个城市。

（2）In a pinch, you could get home on foot.

       在万不得已时, 你可以步行回家。

5. on guard 站岗,值班

（1）Two soldiers must be on guard all night.

       必须有两个士兵撤夜站岗。

（2）Put none but Americans on guard tonight.

       今夜只让美国人担任警戒。
 

【练习】

英译中：

（1）The officers on duty were visibly overcome, many of them in tears.

（2）What on earth are you hinting at?

（3）He suddenly cried out that the storehouse was on fire.

（4）Some people came by car, others came on foot.

（5）The sentry is on guard.