Describe why it is said that all life depends on autotrophs/producers.

because they are the ones able to harness free energy such as the sun and store it in sugars and other biological chemicals such as fats and proteins. other creature like us eat them to gain our energy so without them we would all starve

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.