Answer:
Step-by-step explanation:
A control group is a standard group which is used for the purpose of the experiment. It does not receive any manual treatment by the experimenter. Instead it is kept as a standard for comparison of the other variables.
The multiple control groups are used in the experiment so as to increase the accuracy, consistency and reliability of the results. As if one control group contains contaminants it may produce errors in the experiment. To avoid error and enhance error and increase accuracy multiple control groups are used.