In the context of outside influences on research, what is the difference between maturation and attrition?

A. Maturation is the decrease in the number of subjects studied over time; attrition is the change in subjects over time.
B. Maturation is the change in subjects over time; attrition is the decrease in the number of subjects studied over time.
C. Maturation is the change in subjects over time; attrition is the change in subject responses due to world events.
D. Maturation is the change in subject responses due to world events; attrition is the change in subjects over time.

help please!!