The Nurse Is Critiquing a Research Study That Involves Subjects

The nurse is critiquing a research study that involves subjects undergoing chemotherapy for breast cancer. Which finding would meet a criterion for inferring causality between performance of exercise and adaptive behavior of the subjects receiving chemotherapy?

A) Adaptive behavior began before the exercise program was initiated.
B) Adaptive behavior occurred in the control group over time.
C) The level of adaptive behavior increased in direct proportion to an increase in the intensity of the exercise.
D) No difference in adaptive behavior was observed between subjects in the experimental group and subjects in the control group.