Birds in outside cages develop immunity to airborne bacteria.

养在户外笼子里的鸟对空气传播的病毒有免疫力。

The disease develops mostly in children since they have less natural immunity than adults.

这种病绝大部分在儿童身上发作，因为他们的自然免疫力不如成人。

The police are offering immunity to witnesses who help identify the murderers.

警方对帮助他们指认杀人凶手的证人免予起诉。