A Controlled Experiment ________

A controlled experiment ________.

A) is repeated many times to ensure that the results are accurate
B) proceeds at a slow pace to guarantee that the scientist can carefully observe all reactions and process all experimental data
C) includes at least two groups, one of which does not receive the experimental treatment
D) includes at least two groups, one differing from the other by two or more variables
E) includes one group for which the scientist controls all variables