Why Is It Essential That the Experimental and Control Groups

Multiple Choice

Why is it essential that the experimental and control groups be treated identically in every respect but one?

A) so that the dependent variable can be accurately measured
B) so that the results will apply outside the laboratory setting
C) so that if the behaviour of the two groups differs,the difference can be credited to the one thing that distinguished the groups from one another
D) so that if the behaviour of the two groups differs,the difference can be used to establish a functional relationship between the independent and dependent variables