A cognitive psychologist is interested in whether increasing reading speed reduces comprehension. She has students complete a reading comprehension task before and after a six-week speed-reading course. In the beginning of the study, a randomly selected group of 81 students scored an average of 107 points on the reading comprehension task. Since the sample size is larger than 30, the cognitive psychologist can assume that the sampling distribution of MD is normal. She plans to use a repeated-measures t test. The cognitive psychologist identifies the null and alternative hypothesis as: