Answer: e. An experiment imposes treatments on the subjects, but an observational study does not.
Step-by-step explanation:
Experiment is scientific procedure that is undertaken by an individual or a researcher in order for the person to either make a discovery, or test a hypothesis.
Observational studies are the studies whereby the researchers just observe the impact of a treatment or risk factor e.g. cohort studies. In observational study, the researchers just collect data based on what they've either heard or seen and they've no control over such variables collected whole for an experiment, treatments are applied to a group and the effects are recorded.
