他收到了一封威胁信，如果不付钱就会伤害他的家人。

He got a letter with a ___threat to harm his family unless he paid the money.

这些害虫对农作物构成了严重威胁。

These pests are a serious ___threat to the crops.

低气压是暴风雨即将来临的征兆。

The low pressure is a ___threat of an approaching storm.