The correct answer is D. Multi-stage sampling.
A restricted random sampling technique is a sampling technique in which the sample is selected from a subset of the population. This means that not all members of the population have an equal chance of being selected for the sample.
Stratified sampling is a restricted random sampling technique in which the population is divided into groups, or strata, and then a random sample is selected from each stratum. This ensures that all strata are represented in the sample.
Simple random sampling is a non-restricted random sampling technique in which each member of the population has an equal chance of being selected for the sample.
Systematic sampling is a non-restricted random sampling technique in which every nth member of the population is selected for the sample, starting with a randomly selected member.
Multi-stage sampling is a sampling technique in which the population is divided into groups, or stages, and then a random sample is selected from each stage. This is a more complex sampling technique than the other techniques listed, and it is often used when the population is large or difficult to access.
In conclusion, the correct answer is D. Multi-stage sampling.