A self-possessed person is one who is very assured of his or her own capabilities, is quite calm and collected, and just generally cool.
Having this in mind, the way that the character of the niece can be described is B. confident.
The other options don't make much sense here.
Last sentence: 'earning their creators...' should be 'its creators'. and 'our intended landing point' should be its intended landing point.
Also, you might want to consider whether the last sentence borders on being a run-on, and whether breaking it into two sentences might not enhance readability.
I would say D. because all of the others are basically answering the entirety of the speech. If you would discuss ways to increase the literacy rates in the U.S. you would need to go over it last after you explain why the U.S. is so illiterate.
That’s it will be with the battery of kelvin