immune to: 对；不受……感染Not to be left behind are the disease-spreading pests, about 100 species of which have become immune to a variety of insecticides now in use.传播疾病的害虫也不甘落后，其中约有100种对目前使用的各种杀虫剂有了免疫力。
free from: 使摆脱；免于；解放These animals could at any time break free from their ropes.这些动物可以随时从捆住他们的绳索中挣脱出来。
