The Main Reason That Humans Are One of the Few

The main reason that humans are one of the few species to have long,committed relationships is that:

A) human infants are born before they are fully developed and thus need a lot of care.
B) we are the most socially complex of all species and thus need a partner to help us perform many socially important tasks.
C) the stability of a monogamous relationship allows us to focus on our jobs and careers.
D) societal pressures to choose and remain with a mate are enormous.