Answer:
D) Both A and C are correct.
Explanation:
If the sample contains 50 students, the percentage equivalent to each student is:
![P = (100\%)/(50)=2\%](https://img.qammunity.org/2020/formulas/mathematics/college/3y2xl6jckdyhe1krwz8acjqj3ag90hi3ky.png)
Each student corresponds to 2%, which means that percentages should be multiples of 2%.
21% is not a multiple of 2% and corresponds to:
![n = 0.21*50 = 10.5](https://img.qammunity.org/2020/formulas/mathematics/college/ywqt26gjdf1vn7l1505m280y17j7a786d3.png)
21% of 50 students is 10.5 students, and you cannot sample a fraction of a student.
Therefore, Both A and C are correct.