ATP synthase is

Aboth an enzyme that makes ATP and a channel protein, and helps hydrogen ions cross the thylakoid membrane.
Bboth an enzyme that makes ATP and a channel protein, and helps hydrogen ions cross the chloroplast inner membrane
Cboth an enzyme that makes ATP and a carrier protein, and helps hydrogen ions cross the thylakoid membrane
Dboth an enzyme that make ATP and a carrier protein, and helps hydrogen ions cross the chloroplasts inner membrane.