Researchers studied how raising the concentration of an antibiotic affected the development of antibiotic resistance in bacteria. Four bacterial groups were cultured, and each group received a different antibiotic concentration. For each group, the number of resistant bacteria and the total bacterial population were recorded at intervals over 24 hours. The graphs present the findings. The antibiotic concentrations shown are $0\,\text{mg dm}^{-3}$, $90\,\text{mg dm}^{-3}$, $215\,\text{mg dm}^{-3}$ and $600\,\text{mg dm}^{-3}$. The bacterial population is measured as $\times 10^6$. Which statements are valid conclusions that can be drawn from these results?
- A1, 2 and 3
- B1 and 2 only
- C1 and 3 only
- D2 and 3 only