The Main Reason That the Transition to Adulthood Is Lengthening

The main reason that the transition to adulthood is lengthening is that young adults today

A) are less mature and lazier than their earlier counterparts.
B) have a longer life expectancy, meaning that every period is longer.
C) require more time to educate themselves in order to become self-sufficient.
D) need to live up to stricter standards of what it means to be an adult.