警卫时刻保持警惕。

The guard remains ___vigilant.

保安在夜间保持高度警惕，以确保商场安全。

The security guards remain ___vigilant at night to ensure the mall's safety.

父母需要对孩子在网上的活动保持警惕。

Parents need to remain ___vigilant about their children's online activities.