Twenty people participate in a weight-loss program for two months. Their weights after the two months are compared to their starting weights. What kind of mean difference might we expect if the null hypothesis is true for a 2-tailed paired- samples t test? Weight loss, indicating that the program does not work A negative mean difference, indicating significant weight loss O A loss of pounds, on average, showing the effectiveness of the program No change in weight or weight gain, indicating that the program does not work