Suppose that the midterm marks for a course are (approximately) normally distributed with a mean of 12 marks (out of 20 marks) and a standard deviation of 4 marks. Assume that the top-performing student has a z-score of 2.5. This means: Select one: O a. The student's mark is 2.5 standard deviation above the mean midterm mark O b. The student's mark is in the 25% percentile O c. The student's mark is 2.5 standard deviation below the mean midterm mark O d. The student's mark is 2.5 times higher than the second best-performing student