—Do you know the artist _______ the judges gave a prize?

—Yes. He is the teacher _______ I have been taught painting for two years. [ ]

A. to whom, by whom

B. for whom, by whom

C. to whom, form whom

D. for whom, on whom

当一氧化碳和氮氧化物共存时，两者毒性均增加，这种情况称为毒物的（）

A.相加作用

B.相乘作用

C.拮抗作用

D.独立作用

E.竞争作用