Which of the Following Yields a Cluster Sample

Multiple Choice

Which of the following yields a cluster sample?

A) All students in a class are divided into groups of 15.One student is randomly chosen from the 1st group,the remaining observations are every 15th student thereafter.
B) The best 15 students,according to the opinion of the instructor,in a class are selected.
C) All students in a class are grouped according to their gender.A random sample of 8 is selected from the males and a separate random sample of 7 is selected from the females.
D) All students in a class are divided into groups according to the rows that they are seated.One of the groups is randomly selected.