Bea is 70 years old and works part-time at a discount store. She keeps herself engaged by participating in various activities she enjoyed during middle adulthood. She volunteers occasionally at a local food bank and relishes spending time with her family and the members of her bridge club. According to the ______ theory of aging, Bea is aging successfully.

A) Activity
B) Kubler-Ross
C) Disengagement
D) Wear-and-tear