How Do the Rules of Endogamy Function in Society

How do the rules of endogamy function in society?

A) They tend to maintain social distinctions between groups.
B) They encourage the extension of affinal bonds to an ever-widening circle of people.
C) They prove that the incest taboo is not the cultural universal it was once thought to be.
D) They extend kin ties across classes.
E) They expand the gene pool.