Why is it important that an experiment include a control group? a) a control group assured that an experiment will be repeatable. b) without a control group, there is no basis for knowing if a particular result is due to the variable tested or to some other factor. c) the control group is the group that the researcher is in control of; it is the group in which the researcher predetermines the nature of the results. d) the control group provides the reserve of an experimental subjects.