This is the name for water outside of cells and makes up 1/3 of body fluid.

c. is the correct answer

sorry to break it to ya but no one can answer your question it's just

jk but i am serious about the part that most people cant answer it beacuse you did not mention the section you are talking about. but it would if you added some detail and were a bit more specific.

i'd have to say the answer is probable the second option "the geosphere interacting with the atmosphere"