Identify the type of sampling used;systematic, convenience, stratified, cluster, or none of them.

a)-At a police sobriety checkpoint, every 3^rddriver is stopped and interviewed

b)-I randomly select 10 students from each statistics class at MCC.

c)-I randomly select 3 statistics classes at MCC and interview all of the students in those classes.

d)-I set up a table in the MCC cafeteria and interview the 30 students