Date X cleanser Y cleanser none
5/18/11 0 0 0
5/19/11 0 0.25 0.50
5/20/11 0 1.0 1.25
5/21/11 0.20 2.75 3.0
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Which of the following is a constant, or control variable, in this experiment?
The brand of cleanser that didn't work. (MY ANSWER)
The results observed over four days.
The brand of cleanser that worked best.