After hiking all morning, rafael and his friends needed a rest, so they sat down on a large rock and ate their lunches.

how would this sentence be corrected?

a.) after hiking all morning, rafael and his friends needed a rest so they sat down on a large rock and ate their lunches.
b.) after hiking all morning, rafael and his friends needed a rest. so they sat down on a large rock and ate their lunches.
c.) the sentence is correct as is.