Answer:
a. By Calculating magnetic reversals.
Explanation:
They determine the age of the ocean floor by examining magnetic fields in the planet Earth.
Mammals are adapted to live in D - all of the above. Mammals are, infact, very versatile groups of species which have evolved in a way that also itself enables their versatility. For this reason, mammals have been able to roam the different parts of Earth and thrive in that environment.
Slightly movable is the answer