Burning of fossil fuels has changed the atmosphere by a) producing a hole in the ozone. b) reducing the cfcs in the atmosphere. c) increasing the concentration of carbon dioxide. d) increasing the concentration of ozone in the atmosphere

The answer is Increasing the concentration of carbon dioxide in  the atmosphere. 
Greenhouse gas are contributing to global warming because they trap more of the sun's energy in the Earth's atmosphere. The smoke released from the burning of fuels is a green house gas. Our dependence on burning fossils fuels, and releasing the carbon dioxide in them we are adding a lot more carbon dioxide to the air.

Because the carnivores keep the herbivore population in check