d Separate the students by homeroom assigned each homeroom h

d. Separate the students by home-room assigned (each home-room has 25 students). Pick a random sample of four home-rooms. If a home-room is selected, all students in that home-room are included in the sample.

Cluster Sampling.

We are separating the students based on home-room assigned. So, we are making clusters based on home-room. The sample is no more completely random.