What Is the Primary Difference Between Unilineal and Ambilineal Descent

What is the primary difference between unilineal and ambilineal descent?

A) unilineal allows the individual and family an opportunity to affiliate with mother's or father's lines
B) ambilineal allows the individual and family some flexibility in choosing the descent group
C) unilineal and ambilineal are much the same, except in ambilineal descent there are stricter rules about allegiance
D) there is no known difference between these two systems