Based on Experiment 1, at a concentration of 10 mM, which drug was most effective at killing bacteria?
A. Drug R
B. Drug S
C. Drug T
D. Drug V

Experiment 1

Equal numbers of penicillin-resistant bacteria were put into flasks containing 10.0 milliliters of a nutrient medium. The flasks were incubated for 1 hour at 37◦C with different concentrations of the 5 drugs shown in Table 1. A control consisted of bacteria incubated in the medium without any drugs. The bacteria were washed to remove residual drug traces and grown on nutrient agar plates for 7 days. During this time, the bacteria reproduced, forming colonies, which were then counted at the end of the seventh day. Plates with more colonies were assumed to have more live bacteria at the end of the 1-hour incubation period. Table 1 shows the number of colonies counted. The drug-free control showed 50 colonies at the end of 7 days.

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Drug R S T U V Table 1 Drug concentration 10 15 Number of colonies: 26 5 41 42 45 47 50 29 35 38 40 9 12 20 21 22 Notes: *mM is micromolar (mm) 25 0 2 5 6 7 Numbers of colonies are averages for 5 replicates (identical samples).