Suppose you are interested in knowing the average weekly allowance of children who attend the Maplewood elementary schools. You take a sample of students by first taking a random sample of six classrooms and then taking a random sample from each selected classroom. This is an example of what kind of sampling design?
A. systematic sample with random start
B. single-stage cluster sample
C. stratified random sample
D. simple random sample
E. two-stage cluster sample