The best answer would be A: plants and animals were domesticated. The agricultural revolution primarily refers to the period when humans transitioned from nomadic lifestyles of hunting and gathering to settled agricultural communities, leading to the domestication of plants and animals.
While human populations did increase as a result of agriculture, it is not accurate to say that human populations generally decreased due to disease during the agricultural revolution; in fact, settled agriculture often allowed for population growth. Therefore, option D: Both a and c would not be correct.
So, the clear choice is A.