Which of the following statements is true about cluster sampling? Once clusters are selected, participants are randomly selected from those clusters.

Cluster selection does not have to be random, as long as each chosen cluster is randomly sampled.

Cluster sampling uses clusters, which are homogenous groups in regard to characteristics being studied.

Participants within clusters usually live within close proximity, which saves time and money for data collection.

I think it's (D) Participants within clusters usually live within close proximity, which saves time and money for data collection.