What is the primary difference between an experiment and an observational study?

a. experiments are always done in a lab.
b. in an experiment, the researcher manipulates a variable.
c. an observational study involves many more people.
d. observational studies always make correlations.

a experiment study  in which a treatment, procedure, or program is intentionally introduced and a result or outcome is observed

a observational study is a attempt to understand cause-and-effect relationships. However, unlike experiments, the researcher is not able to control (1) how subjects are assigned to groups and/or (2) which treatments each group receives

i hope this helps you -Lazerpony

C will be the correct one