The principle difference between point source and nonpoint source water pollution is
a. whether the pollution is organic or inorganic
b. the number of sources of pollution
c. the amount of pollution
d. whether it is from commercial or agricultural sources

Number of sources of pollution

Ibelieve the answer is relative humidity  because it makes more sense that way. solar flares usually occur in space it doesn't affect the earth, well it could but it wont make a significant damage.  latitude is land it doesnt do anything. prevailing winds, i dont know the correct meaning for this but i doubt that affects the land so it has to be relative humidity.