How Do the Rules of Endogamy Function in Society

How do the rules of endogamy function in society?

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