A middle school has 220 students in grade 6;
170 students in grade 7; and
100 students in grade 8.

The media specialist wants to know which books are the most popular among the students in her school. Since she cannot ask all the students, she will survey a group of them.

Which sample can best help the media specialist draw conclusions about the preferences of all the students in the school?

A. 45 sixth graders, 35 seventh graders, 20 eighth graders

B. 20 sixth graders, 35 seventh graders, 45 eighth graders

C. 45 sixth graders, 45 seventh graders, 45 eighth graders

D. 20 sixth graders, 20 seventh graders, 20 eighth graders​