The answer should be evolutionary theory, good luck!
A.D means in our time (Anno Domini, the year of our lord) and B.C means Before Christ - these two and the other mentioned words are used to B. refer to periods of time.
"De facto" means "in fact, factually" - that something is, indeed, taking place. It is customarily used to denote a situation which is not dictated by law ("de jure") but which happens anyway - so the best answer is A. Law - this segregation is not required by law, but it takes place anyway, for example for financial reasons.
During the free banking era, between 1837 and 1863,banking in the United States was dominated by "<span>a. small, independent bank with no charters," since this was before the larger banks began to issue more and more credit. </span>