The difference between an observational study and an experimental is that. A- In an observational study, only one group is studied, and in an experiment , two groups are studied.
B- is an observational study, the researchers do not control treatment , and in an observational study, it is not.
C- in an experiment , cause and effect is analyzed, and in an observational study, it is not.
D- in an experiment, one group is studied over a short period of time, and in an observational study, the group is studied over a longer period of time.