Maria Ivosevic Married for the First Time at Age 39,and

Maria Ivosevic married for the first time at age 39,and at age 40 she is pregnant for the first time.She is now considering starting college to become a computer systems engineer.When Maria laughingly tells her friends,"I have never done anything when I was supposed to," she is referring to

A) the social clock.
B) the biological clock.
C) the critical period.
D) social norms.