A psychologist administers a test of reflex times to men and women. In the study, the reaction speed to an electrical shock stimulus was measured for a sample of men and for a sample of women. The researcher thinks there may be a difference between men and women in this response.  Let \mu(M) be the average reaction speed for all men. Let \mu(W) be the average reaction time for all women. Which of the following is the null hypothesis of interest in this study?