27 Air pollution can be as harmful to one's health___________28 Traveling on an undergroun
27 Air pollution can be as harmful to one's health___________
28 Traveling on an underground train can reduce exposure___________
29 Pollution levels are lower__________
30 It's wise to stay away from heavy traffic____________
A on the downwind side
B during rush hours
C in spring and autumn
D to toxic air
E between autumn and winter
F as exposure to nuclear radiation