keep a check on的用法和樣例：
例句
- He sent out a party to spy the enemy.
他派出一個小分隊暗中監視敵人的行動。 - We must keep these people under close surveillance.
對這些人我們要嚴密監視。 - The plumber made a careful check of the pipes.
管子工對管道做了仔細的檢查。 - I had a medical checkup before going abroad.
我在出國前作了一次體格檢查。 - You should learn to keep your temper under control.
你應該學會控制自己的脾氣。 - She's really had him on a string.
她真的已完全控制了他。
