Option C. the larger A pairs with the smaller T, and the larger G pairs with the smaller C.
I would think A - Volcanic eruptions can cause both global warming and global cooling.
I personally think it’s carbohydrates
Natural selection is when certain environmental qualities cause a species to evolve in order to survive in the environment. Natural selection is a specific part of that, when some of the variations of the species die off because they can't survive, then the ones who survive live to create more living babies with the qualities that allow them to survive in the environment.