on guard

形容词 on guard:

1. vigilant
   同义词：on one's guard, upon one's guard, on your guard

1. The citizens were warned to be on guard against a sudden night attack.
   市民们得到通知，要提防夜间的突然袭击。
2. Be on guard when somebody flatters you.
   有人奉承你时，一定要当心。
3. There are soldiers on guard at the gate.
   大门口有士兵在守卫。
4. While danger threatens we must all be on guard.
   危险正逼近，我们必须保持警惕。