A Description of a Cluster Sample Might Be ______

A description of a cluster sample might be ______.

A) people who respond to a mailed survey make up the sample
B) all students who sign up for a study make up the sample
C) 60% of the population is left handed so 60% of the subjects chosen are also left handed
D) subjects are selected from a local preschool class to represent preschoolers who live in the area