Why does Winston regard O'Brien as a friend even though O'Brien is his torturer?

a.

Winston believes that O'Brien truly understands him.

c.

Winston is convinced O'Brien respects his defiance.

b.

O'Brien shows remorse whenever he shocks Winston.

d.

O'Brien spares him from the agony of a quick death.

The correct answer is: a. Winston believes that O'Brien truly understands him.

Indeed, even while torturing Winston Smith, O'Brien tells him that he appreciates his mind because it is very similar to his; although he also adds that the issue with Winston's mind is that it is insane, meaning that it is insane because it actually thought the Party could be defeated.