A student is doing a study on study habits. He needs a random sample of students from every grade level. What is a good way to do this?

A)
He could send a questionnaire to every student in Algebra I.

B)
He could put a questionnaire on all cars in the senior parking lot.

C)
He could send a questionnaire to every student in a senior English class.

D)
He could poll all students in a 9th grade, 10th grade, 11th grade, and 12th grade English class.