Explanation: The three-finger G, open-string guitar chord: 6th string: Use the 2nd finger to play the 3rd; 5th string: Use the 1st finger to play the 2nd fret. 4th string: Play open. 3rd string: Play open. 2nd string: Play open. 1st string: Use the 3rd finger to play the 3rd fret. The three-finger C, open-string guitar chord: 6th string
The answer to your question is C.
