密切注视

• keep close watch on
• keep an eye on ...
• watch out
• keep both eyes open
• keep a close watch on
• kept a close watch on
• keep both eyes peeled
• keep both eyes skinned

例句

1. 海关检查员正密切注视着钻石走私犯的活动。
   The customs inspector was on the watch for diamond smugglers.