The difference between an observational study and an experiment is that

While experimenting researcher can record, test or control the group and while observational study researcher can't do that

Explanation:

An experimental study can be under the control of someone who is doing the research or experiment.

The researcher can also manipulate the experiment and in the observational study, there are no experiments.

The observational study requires the research observing of something, this observing includes what happened in the past, what is saw in the past and what is now.

answer; ///he could not explain why the continents drifted;

answer; night terrors;