People are concerned about the quality of the air they .A. hear B. eat C. drink D. breathe

问题补充：

People are concerned about the quality of the air they .

A. hear

B. eat

C. drink

D. breathe

答案：

A. hear

B. eat

C. drink

(答案→)D. breathe

解析：句意:人们都关心他们呼吸的空气的质量。Hear听见； eat 吃； drink喝； breathe呼吸。根据句意故选D。