Which letter replaces the question mark?

A cab driver picks up a nun. She gets into the cab, and the cab driver won't stop staring at her.
She asks him why he is staring.
He replies: "I have a question to ask you, but I don't want to offend you".
She answers, "My son, you cannot offend me. When you're as old as I am and have been a nun as long as I have, you get a chance to see and hear just about everything. I'm sure that there's nothing you could say or ask that I would find offensive."
"Well, I've always had a fantasy to have a nun kiss me."
She responds, "Well, let's see what we can do about that. But first, you have to be single and you must be Catholic."
The cab driver is very excited and says, "Yes, I'm single and Catholic!"
"OK" the nun says. "Pull off to the side of the road, "maybe we will see what we can do."
The nun plants a whopper of a kiss on the cabbie! But when they get back on the road, the cab driver starts crying.
"My dear child," said the nun, why are you crying?"
"Forgive me, but I've sinned. I lied. I must confess, I'm married and I'm Jewish."
The nun says, "That's OK, my name is Kevin and I'm going to a Halloween party."