What is the primary reason for including a control group within ...

[Hawke]

What is the primary reason for including a control group within the design of an experiment?
A) To ensure that the results obtained are due to a difference in only one variable
B) To ensure that the experimenter can perform a more complete statistical analysis
C) To demonstrate in what way the experiment was performed incorrectly
D) To accumulate additional facts that can be reported to other scientists
E) To test the effect of more than one variable

[Melanie]

I think the answer is: A