Which of the following is most acidic?

Option D is the correct answer.
A methoxy group is mesomeric donating (+R) and inductive withdrawing (-I). We know that the +R effect is predominant over the -I effect. But +R effect is only valid when the substituent is at the ortho and para position.
We also know that addition of Electron donating groups to the Benzene ring in phenol decreases its acidity while the addition of Electron withdrawing groups increase it.
By that logic, m-Methoxyphenol is a stronger acid than phenol as the $-OC{H}_3$ group at m-position imparts only -I effect to the ring.