In this task, you are given two facts, and a multiple-choice question. Based on the given facts, answer the question with index of the correct option (e.g, "A").

Fact1: Flowing water can slowly dissolve carbon in sedimentary rock., Fact2: Water falls from the sky and flows downhill due to the force of gravity., Question: What moving downhill due to the force of gravity can dissolve carbon in sedimentary rock? (A) river (B) Raft (C) pebbles (D) rain (E) water (F) sand (G) oxygen (H) craters
E