Which of the following would be the best title for the passage

A．One is considered to have reached adulthood when he has a driver's license.
B．One is not free from the restrictions of child labor laws until he can join the army.
C．No one can marry without the permission of his parents until the age of twenty-one.
D．In the late 19th century in the United States the dividing line between adolescence and adulthood no longer existed.

A．the prolonged period of adolescence
B．the significance of socio-economic status
C．society's definition of maturity and adulthood
D．the gradual acquisition of the adulthood privileges