A research study finds that a group of participants who received relaxation training had lower exam anxiety scores than a group who did not receive training. However, the researcher suspects that the...

A research study finds that a group of participants who received relaxation training had lower exam anxiety scores than a group who did not receive training. However, the researcher suspects that the difference between groups may be caused by the fact that the participants in one group are generally smarter than those in the other. This study has a problem with

a. internal validity.

b. external validity.

c. experimental validity.

d. correlational validity.