What else should the second group of researchers measure to test its hypothesis?
OA.
the current levels of water in the river
ОВ.
the type of pollen in cores from a nondrought period
the composition of microscopic charcoal released during natural
fires
OC.
OD.
the quantities of sediments in cores from the delta during a
nondrought period

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.

Yes yes yes very good