Answer:
The type of sampling used in Jankowski's study of gangs is Option D. Stratified sampling.
Step-by-step explanation:
With stratified sampling, the researcher will partition the population into different groups, usually based on some characteristic that is common to that group. In this case, it was the different kinds of gang membership. Then, the researcher will take a sample of people within each specific group using another sampling method like simple random sampling for instance. The groups that are used in stratified sampling are called strata. Another example would be a national survey that is divided into strata of the different major ethnic groups that comprise the national population.