A college professor wants to survey a sample of students taking his course. Here are some details about his course: He teaches 5 sections of the course.
There are 250 total students across those sections.
There are 50 graduate students and 200 undergraduate students taking the course.
Each section has about 50 students (some graduate and some undergraduate).

The professor wants to take a sample of 30 students for a survey. He suspects that opinions on the survey may differ the most based on student type (graduate or undergraduate), so he wants to design his sample to take that into account. Which of these strategies will accomplish his intended design?

a. Randomly select 6 students from each section for the survey.
b. Randomly select 6 graduate students and 24 undergraduate students for the survey
c. For each section, randomly select one of the first 8 students to arrive to class, and every 8th student thereafter to take the survey.
d. Randomly select one of the sections and give the survey to every student in that section