The rising unemployment was the most important ________ at Congress.

A．issue

B．question

C．problem

D．plan

饮用水的消毒剂有多种，其中杀菌能力强且又不会影响水质的理想消毒剂是（）.

A.液氯

B.漂白粉

C.臭氧

D.石灰