Answer:
b. ex post facto or quasi-experimental.
Explanation:
An ex post facto search is done when a researcher cannot manipulate one of the variables such as sexual behavior or smoking (as described in the question), ie this type of research is done when it is not possible to manipulate the independent variables as they already arrive ready for research. Ex-post fact research deals with variables that are unmanipulated in nature. Quasi-experimental research can also be done for this same situation.
