一个阅读里的语法现象

observer

although these outputs are environmentally hazardous, some plants still generate them as waste products despite the high compliance costs they impose. 请问they指代什么，应该是outputs, 可是outputs cannot impose cost to plants, should this verb be 被动. ?

谢谢！

mjiirggh

我觉得these outputs可以impose compliance costs呀，为什么楼主觉得不行？