I’d like to do something for you_____ everything you have done for me.

A．in exchange

B．in turn

C．in return for

D．in terms of

CO中毒开始出现昏迷时是什么性质的中毒（）。

A.轻度中毒

B.重度中毒

C.中度中毒

D.迟发型脑病

E.慢性中毒