Which of the following is the major cause of global warming ?

The correct option is B

Reflection of IR rays by $C{O}_2$ and $H_{2}O$

The primary greenhouse (heat-trapping) gases in the earth's atmosphere are water vapour ($H_{2}O$), carbon dioxide ($C{O}_2$), methane ($C{H}_4$), nitrous oxide ($N_{2}O$, and ozone ($O_3$). When the radiations of the sun reach the earth, some of these IR radiations are reflected from the surface of the earth. While some of the radiations pass through the atmosphere, rest is absorbed and re-emitted by the greenhouse gases. The excess of absorption and re-emission of IR radiations by the greenhouse gases increases the overall temperature of the earth, thereby causing global warming.