Which of the following is a weakness in the design of Experiment 3?
A. Different amounts of yeast were used in each test tube.
B. Varying concentrations of sucrose were used.
C. There was no control group in which the experimental treatment was not applied.
D. All possible combinations of nutrients were not tested.

Experiment 3

Eight more test tubes were filled with .4 grams of yeast and a 15% sucrose solution. Various combinations of ammonium sulfate, potassium dihydrogen phosphate, minerals, and vitamins were added to the test tubes. Carbon dioxide levels were measured after one and two days. These levels are shown in Table 3.

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1 2 3 4 in 5 6 7 8 Sucrose (%) 15 15 15 15 15 15 15 Table 3 Other materials added (NH2)2SO4, KH₂PO4 (NH₂)2SO4, KH₂PO4, minerals (NH₂)2SO4, KH₂PO4, vitamins (NH2)2SO4, KH₂PO4, minerals, vitamins minerals vitamins minerals, vitamins CO₂ (mm) Day 1 19 28 31 100 3 0 0 4 CO₂ (mm) Day 2 38 40 52 100 12 14 5