Clouds release moisture on the of mountains.
a. windward side
b. leeward side
c. peaks
d. slopes

c. peaks

Clouds part of the hydrosphere release moisture at the peaks of mountains.
Hydrosphere includes the total mass of water on the surface, underground or over the surface of earth. About 75% of the earth’s surface are covered by oceans and so a huge part of our planet is covered in water and so hydrosphere is an important aspect. Hope I have answered your question as per your asking. 

Writing, you can revisit previous parts of the lesson by returning to the course map. be sure to refer to the lab’s student guide, which you can find on the first page of the lab experiment activity