A sample of midterm grades for five students showed the following results: 68, 61, 78, 86, 72. Which of the following statements are correct, and which should be challenged as being too generalized?

(a) The average midterm grade for the sample of five students is 73.
(b) The average midterm grade for all students who took the exam is 73.
(C) An estimate of the average midterm grade for all students who took the exam is 73.
(d) More than half of the students who take this exam will score between 66 and 81.
(e)If five other students are included in the sample, their grades will be between 61 and 86.