This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
The type of sampling where the individual himself introduces the other subjects of surgery is called as: 
Select and explain. 
A. Systemic sampling, B. Snowball sampling, C. Introductory sampling, D. Successive sampling
B: Snowball sampling
Answer: B: Snowball sampling 
Explanation: Snowball sampling is a technique for developing a research sample, where existing study subjects recruit future subjects from among their acquaintances.
It is a type of non-probability sampling.
This sampling technique is often used in hidden populations which are difficult for researchers to access; example, drug users or commercial sex workers.
Thus, the sample group appears to grow like a rolling snowball.
Because sample members are not selected from a sampling frame, snowball samples are subjected to numerous biases.