Fifteen people will be enrolled in a four-week foreign language course. On the first day, the instructor gives the students an exam to determine how much they already know. At the end of the four weeks, the instructor gives the students the same exam again. From the exam scores, the instructor wants to determine if taking the course has significantly increased the students' foreign language ability. Which of the four cases in Chapter 10 does this problem fall under or represent? A. Case I - Use z statistic with known population variances

B. Case II - Use t statistic, assuming variances are unknown but equal C. Case III -Use t statistic, assuming variances unknown and unequal D. Case IV - Use paired t test