问题补充：
— If there are people driving, there will be air pollution.
— Yes, the air will be fresher.
A. less; less
B. less; fewer
C. fewer; fewer
D. fewer; less
答案：
A. less; less
B. less; fewer
C. fewer; fewer
(答案→)D. fewer; less
解析：根据后文people 为可数名词复数，pollution为不可数名词，又根据需要，要用比较级，故选D
