The question was: All values in the 95% confidence interval are negative. This means that:
Your Answer: the value of t should be squared.
Answer and explanation: Your answer is incorrect. Since the mean difference is the pain experienced by the treatment group minus the pain experienced by the control group, a negative value indicates the experimental group was in less pain. Since all values in the confidence interval are negative, this means it can be inferrred that, in the population, the treatment is better than the control.