Experiment: leo placed two circles of paper in a petri dish (something used for growing bacteria). one circle of paper was soaked in penicillin. the other had nothing on it. he poured a liquid filled with bacteria into the petri dish which covered both papers. both circles of paper were placed in the petri dish about 3 cm apart. at the end of the experiment, there were no bacteria growing in the circle soaked in penicillin. the other circle of paper had bacteria that were growing well. what was the control