Which of the Following Best Matches the Description

Which of the following best matches the description?
-Substances released into the atmosphere,which in their unmodified form are a health risk.

A) thermal inversion
B) acid deposition
C) secondary air pollutants
D) ozone
E) particulates
F) radon
G) greenhouse effect
H) primary air pollutants
I) radon.
J) photochemical smog
K) oxides of nitrogen
L) sulfur dioxide