Experimental Mortality Refers to a Source of Confounding in Which

Experimental mortality refers to a source of confounding in which:

A) age or fatigue affects the experimental results.
B) subjects are selected on the basis of their extreme scores on a measure.
C) subjects drop out of a study more often in one condition of the experiment than in another because of the effects of the condition.
D) uncontrolled events occur between multiple observations and affect the experimental results.