Four students, 1, 2, 3 and 4, counted how many oxygen bubbles were released during an investigation into the effect of catalase from plant tissue on hydrogen peroxide. Each student repeated the experiment five times and found the mean number of bubbles per minute. Which have correctly calculated the mean? (A table is shown of students, raw data in bubbles minute$^{-1}$, and calculated mean values.)
- A1 and 4 only
- B2 and 3 only
- C1, 2, 3 and 4
- D3 only