Question

Climatologists study ocean currents because they play a major role in global climate.

Answer 1

I think  the correct answer from the choices listed above is option B. It is the atmosphere and the hydrosphere the two parts of the Earth system that a climatologist is involved. Hydrosphere is the oceans and other water bodies. While, the atmosphere plays a major role in the cycle of water here on Earth. So, the two goes together.