A school supervisor wants to determine the percentage of students that bring their lunch to school. Which of the following methods would assure random selection of a sample population?

A.
The supervisor should randomly select one grade level and survey all of the students in that grade.
B.
The supervisor should select one grade level and survey randomly selected students from that grade.
C.
The supervisor should survey all of the students enrolled in the school.
D.
The supervisor should randomly select students from all grade levels taught at the school.