Which theory posits the notion that retirement is a mutually beneficial agreement between two parts of society, the old and the young?
a. activity theory
b. exchange theory
c. disengagement theory
d. conflict theory

The best answer is the disengagement theory!

The desengangement theory (Cumming, Henry, 1961) specifically focuses on the last years of life and sees them as something natural in human life.

The other theories, such as the activity and the continuity theories stress that the older people should remain active and not completely retire.

The theory that posits the notion that retirement is a mutually beneficial agreement between two parts of society would be the conflict theory - D.

The reason for this is that conflict theory posits that different social groups will only function if they create mutually beneficient choices.