B. Considerate
Considerate, adj.
"Careful not to inconvenience or harm others."
Quindlen links the conclusion to the introduction of her essay with the words "like many improbable ideas, when it works, it's a wonder", which is very close to her claim in the overall text, "America is an Improbable idea", it isn't supposed to work but it does despite all of the differences, specifically racial or ethnic, within it.
By a large margin which group made up the majority of Californians population in 1840? D. Native Americans.
Hope I helped, good luck:)
