Over the past 100 million years of Earth history, it is known that the magnetic poles have reversed themselves times.

a and b because with the other three, they simplify to something else.

water: cools down faster, heats up faster, idk the last one

land: cools down slower, heats up slower, idk the last one

edit: if anything i answer is incorrect, i'm sorry. double check my work with someone else before using it. you for understanding.