Jenna wants to learn whether men or women are better drivers. To determine this, she decides that she will measure driving ability by examining the number of automobile accidents people have been involved in as a driver

The number of accidents is the basis of
a. her control group in this study.
b. a theory of good driving.
c. the independent variable in this study.
d. the operational definition of driving ability.
e. a case study examination of driving ability.

d. the operational definition of driving ability.