Which term refers to the ability of an organism to return to its former condition after a period of stress? 

A)  inertia 
B)  constancy 
C)  stability 
D)  resilience

Resilience refers to the ability of an organism to return to its former condition after a period of stress, making it the most suitable choice among the given options. Inertia refers to an object's tendency to resist a change in motion; constancy refers to the ability to maintain a stable internal environment despite changes in the external environment, while stability refers to the ability to maintain a steady state despite slight variations in internal and external conditions.