Dr. Whetstone is curious about how self-esteem changes as a result of a new counseling program. She is concerned about testing threats in her study. Which of the following would you recommend to her as a way to address this type of threat?

a. Refusing to let participants drop out Of the study
b. Using a different measure of self-esteem at pretest than at posttest
c. Conducting a pretest-only study
d. Omitting a comparison group