Verified answer

From this list, the answer is

A) methane

BTW, it is not true that methane (CH4) is more of a greenhouse gas than CO2. This is a myth that is often spread by deniers of anthropogenic global warming, which is caused by extra CO2 emissions due to human activities. If you look at the spectral absorption regions of each of these gases (link below), you can see that CO2 is second only to H2O in its ability to absorb outgoing thermal radiation.

E. None of the above.

Water vapor is the leading greenhouse gas.

Increases in water vapor leads the pack over all others.

people talk about co2 but methane is 16 times worse than co2

so A