Answer: B
Explanation:
In order to get the best representative sample, you should choose the widest range of students, which is from a random sample of all students.
(A) Choosing from only the 6th graders, eliminates the choices the other grade-level students would choose.
(C) Choosing only from students who participate in after-school activities, eliminates the choices the other students would choose.
(D) Chhosing only from students not participating in the fundraiser is silly since you want to know what the students participating in the fundraiser would choose.
The only possible option is B - students from all grades, regardless of whether or not they participate in after-school activities.