Fact 1: Flowing water can slowly dissolve carbon in sedimentary rock.

Fact 2: Water falls from the sky and flows downhill due to the force of gravity.

Given the two facts above, answer the question "What moving downhill due to the force of gravity can dissolve carbon in sedimentary rock?" with the following options: 
- river
 - Raft
 - pebbles
 - rain
 - water
 - sand
 - oxygen
 - craters


 

     water    