Question

a control group is in all experiments.
(1 point)
necessary
optional
variable
experimental

Explanation:

In scientific experiments, a control group is not always required. For example, in some observational studies or certain types of experiments where the nature of the research doesn't demand a direct comparison group (like some qualitative experiments or when using historical data as a reference instead of a contemporaneous control group), a control group may not be present. So it's not a strict necessity in all experiments.

Answer:

optional