Answer:
Option b.
Explanation:
Okay, let us check some important things from this question, we have to break the statement in the question into two parts;
(1). The first statement in the question; ''The researcher is interested in learning if elderly persons perceive their health to be satisfactory even with comorbidities and chronic illness'': this means that the researcher needs LARGE GROUPS OF PARTICIPANTS for his or her research.
(2). The second part; ''... The researcher lists residents in alphabetical order and chooses every third person on the list. To ensure improved generalizability...'' : in this part, the Researcher is choosing 'Randomly' the names of his or her participants in the research.
The method the researcher is using is what is called RANDOMIZATION which means selecting randomly from groups for research purpose.
It's a and b because the question says what types
