Research Summary: Magnesium ribbon burn times. Equal-length magnesium ribbons were burned in four oxygen mixtures and timed in repeated trials. The relevant data display is shown. Columns: Oxygen mixture | Burn time readings (s); Rows: Mixture A | 18.2, 18.5, 18.3; Mixture B | 14.1, 14.3, 14.2; Mixture C | 16.0, 6.8, 16.1; Mixture D | 21.4, 21.1, 21.3. Which interpretation best protects the comparison among mixtures?