Answer:
a. control; experimental
Step-by-step explanation:
A control experiment can be defined as an experiment in which a condition assumed to be a probable cause of the effect is being compared to the same situation by the scientist without involving or using the suspected condition.
On the other hand, an experimental group can be defined as a collection of participants that are subjected to the independent variable.
Most experiments have a control group for purposes of comparison. This group is not given the treatment or the same independent variable as the experimental group.
Therefore, this is the reason why science completely or totally rejects any hypothesis which is not supported by observations, as well as the results obtained from control experiments.
This ultimately implies that, for any hypothesis to be acceptable in science, it must be supported by observations and the results of control experiments; this give rise to factual informations, theories and by extension solutions to problems.