The -ing form can be used as a noun. For example: "reading is my favorite activity in my spare time."
It can also be used as an adjective, for example: "That movie had a very surprising end".
The -ing form can also be used as a verb in the progressive or continuous tense, for example: "I am watching TV now." (I am watching TV at this moment). Or: "I was waiting for him, when she told me he would not come to the party." (The action of waiting was in the past, when I heard he would not come to the party).
Your answer would be B. He's talking about not being able to prove his age because he hasn't never seen a real record of his birth or anything else that would give him an idea of how old he is, so no real way to actually prove it.
Well you start a paragraph with an open ending question so ask about the character then answer that question and do the same for the other one and then compare or explain why they are the main characters and how they contribute to the book