One of the challenges of conducting health research is that it is impossible, and unethical, to manipulate certain variables, such as sexual behaviors or smoking. the research design that examines differences between groups without manipulating these groups isa. experimental.
b. ex post facto or quasi-experimental.
c. random assignment.
d. longitudinal.

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.