keep a watch over

例句：

1. 1. The policeman kepta watch over the crowd during the protest.
   警察在抗议期间对人群进行了监视。
2. 2.The babysitter kept a watch overthe children while they were sleeping.
   保姆在孩子们睡觉时对他们进行了看守。
3. 3. The teacherkept a watch over the class to ensureeveryone was following the rules.
   老师对全班进行监督，确保每个人都遵守规则。