be exempt from 还是 be exempted from 书上是前者,为什么不用被动?

exempt 这个词既是形容词,又是动词
be exempt from 是正确的,它是词组,意思是“被免除,被豁免”,例如：He is exempt from military service.(他被免于服兵役)
exempt 的动词的意思是“免除、豁免”
例如：They made efforts to exempt him from responsibility.他们努力想免除他的责任.