Answer: a. water cycle
Step-by-step explanation:
A water cycle can be define as the cycle of water in which water in various states like solid, liquid and gaseous forms circulates in different spheres of the earth. It describes how water evaporates from the surface of earth, the water vapors accumulate in the atmosphere, these water vapors become cool and condense in the form of rain or other kind of precipitations. The water cycle plays an important role in changing the weather condition of a region.