Most Researchers Agree That, in the United States, the Frequency

Most researchers agree that, in the United States, the frequency of marital coitus

A) increases with age and length of time married.
B) decreases with age and length of time married.
C) shows tremendous variability with age and time with increases among those with higher income levels and decreases among those with lower income levels.
D) is impossible to study since people will not divulge this kind of information.