A principal wanted to survey students who took a standardized college entry exam about how prepared they felt for
the exam. The principal put together a bag of marbles. There was 1 marble for each student, and 20 of the marbles
were red. Each student chose a marble, and those who chose the red marbles took the survey. Which sampling
method was used?
O cluster sampling
simple random sampling
O stratified random sampling
O systematic random sampling