The primary source of increased levels of greenhouse gases on earth is

The primary source of the greenhouse gases on the Earth is the burning of the fossil fuels. The fossil fuels are used for the generation of electricity in the thermal power plants. The fossil fuels are used to power the engines in the various vehicles like the aircraft, cars, bus, trains and trucks. The fossil fuels are also used for conventional heating of the home during the cold season. When the fossil fuels are burned they release smoke that has carbon dioxide, carbon monoxide, and soot in it. These chemicals trap the heat of the Earth leading to global warming.

the answer is b.) hydrogen bonds between bases.