Oxygen (O2) and nitrogen (N2) are: a. the major gaseous byproducts of combustion.

c. the major gases that make up only the troposphere

Explanation:

Oxygen (O2) and nitrogen (N2) are the major gases that make up only the troposphere because both oxygen and nitrogen are heavy gases which is present at lower height so it comes under the troposphere layer while on the other hand, ozone gas that act as a filter for harmful radiation of the sun is present in the stratosphere which is present next to troposphere layer of atmosphere.