【问】 The customs inspector was____for smugglers.

A. on the guard B. on the watch

C. on watch D. on alert(攻读硕士学位研究生入学考试英语试题，84B)

应选B(on the watch)还是应选C(on watch)?

【答】 on the watch (for)的意思是：“密切注视着”、“警惕着”、“对……留神”：

1. Be on the watch;there are thieves about.

要警惕，周围有小偷。

2. Our frontier guards are always on the watch for any enemy who might dare to intrude onour territory.

我边防战士时刻警惕着任何敢于入侵之敌。

on watch的意思是“值班”

1. He was standing on watch. (Palmer)

他在站岗。

2. Who’s on watch now? (LDCE)

谁现在在值班?