Answer:
b) Stratified
Explanation:
Given: A mattress store boasts 4 out 5 sleepers in a commercial that airs locally. I talked to the owner and found out he only talked to ten people.
This is not regressive as regressive got two variables dependent and independent
This is not variation as no variation is explained in the sample
This is not replication, as replication involves repitition of experiments a number of times.
This is not blocking because nothing is blocked in this
So this comes under
b) Stratified