Quote 49
This is what Siobhan says is called a rhetorical question. It has a question mark at the end, but you are not meant to answer it because the person who is asking it already knows the answer. It is difficult to spot a rhetorical question. (127.15)
By now we can understand why rhetorical questions would be confusing to Christopher. Using the same analogy from the previous quote, this would be like someone asking him, "What's sixteen divided by four?" and not expecting an answer. What's different about this example is the last sentence, which reveals a sadness, or weariness, at his confusion.
Quote 50
And I said, "Thank you for supper," because that is being polite. (149.45)
This is a perfect example of the way Christopher has learned to interact through rote memorization of social customs. We can just imagine the lesson: "And then when someone cooks you dinner, you should say, 'Thank you for dinner.'" "Why should I say that?" "Because that is being polite."
Quote 51
I wonder if you can understand any of this. I know it will be very difficult for you. But I hope you can understand a little. (157.15)
This line appears in one of Christopher's mother's letters – the one in which she explains why she left him and his father. After going on at length, with heart-wrenching explanations and recollections, she writes that she realizes Christopher might not be able to understand any of the letter at all, suggesting that she's writing this letter as much for herself (as a release valve, as a way to express her own grief and guilt) as she is to apologize to Christopher.