Answer:
D. cluster
Explanation:
Convenience: Based on availability.
Systematic: The first element is sorted randomly, then the others follow a pattern.
Random: Each member of a sample has the same probability of being sorted.
Cluster: Each group is cluster, and when a cluster is sorted, every member of the group is sample. This is the correct answer.
Stratified: Population is divided into groups and then members from these groups are sorted.