Ozone close to earth's surface in the form of is harmful.
a. hydrogen
b. water vapor
c. smog
d. radon

Smog

Explanation:

Smog is the form of pollutant that consists of nitrogen oxides, sulphur oxides, ozone, smoke and other particulates . During summer smog gets associated with the photo-chemical compounds known as secondary pollutant (which are formed of primary pollutants) which undergo chemical reactions in the atmosphere.

Compound like nitrogen oxides ,  volatile organic compounds go through a series of chemical reactions with sunlight, moisture, and other compounds to produce ground level ozone that further turns into smog

d i think its   answer d

the answer is: metamorphic rocks often show the presence of fossils, also a

hope i

-lavira: )