The correct answer is D

Explanation

The students who receive A’s, B’s, and C’s account for (1 over 5) + (1 over 4) + (1 over 2) of the students, that is, 19 over 20. This leaves 1 over 20 of the students receiving D’s. You know that 10 students receive D’s, so 10 is 1 over 20 of the total. This means that the total number of students is 10 times 20, or 200.