In Which of the Following Situations Is It Most Likely

In which of the following situations is it most likely that maturation is a probable threat to internal validity and should be a special concern when selecting a research design?

A) You will provide a 6-week treatment for a group of depressed clients who have been depressed for a minimum of a year.
B) You will provide a 1-year treatment program for a group of people who have recently (within the past month) lost a spouse to death. You will measure depression as the vehicle of success.
C) You will provide tutoring to a group of at-risk middle school students for 8 weeks and you will compare their grades during the current 8-week grading period to the previous 8-week grading period. These clients have been experiencing poor grades for at least a year.
D) You will measure knowledge of job hunting skills once at the beginning of a 3-hr training session for unemployed clients and again at the end of this training session.