A middle school has 180 students in grade 6; 215 students in grade 7; and 200 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. 27 sixth graders , 27 seventh graders , 30 eighth graders B. 32 sixth graders , 36 seventh graders , 40 eighth graders C. 36 sixth graders , 43 seventh graders , 40 eighth graders D. 32 sixth graders , 36 seventh graders , 30 eighth graders