Which excerpt from Extremely Loud and Incredibly Close reveals a childish tone?

A. Need some more copies?” Walt asked. I gave him a high-five, and I showed him the key that I had found, and asked him what he could tell me about it.

B. “Could be a safe-deposit box, actually. An old one. Or some kind of fire-rtrdant cabinet.” That made me crack up a little, even though I know there’s nothing funny about being a mental rtrd.

C, “Well, hardly anyone uses keys anymore.” “I use keys,” I told him, and I showed him my apartment key. “I know you do,” he said.

D. I said, “I have another question.” “Shoot.” “Do you think I could find the company that made this key?” “Anyone could’ve made it.” “Well then, what I want to know is how can I find the lock that it opens?”