Catalase is an enzyme found in potato tissue. It catalyses the breakdown of hydrogen peroxide into water and oxygen.

hydrogen peroxide  $\underrightarrow {\text{catalase}}$  water + oxygen

The apparatus shown was used to investigate the activity of catalase.

Five identical potato discs were dropped into 15 cm$^3$ of a 3% hydrogen peroxide solution at a temperature of 20°C. The time taken for 5 cm$^3$ of oxygen to be produced was recorded.

This procedure was repeated at each of the following temperatures: 30°C, 40°C, 50°C, 60°C and 70°C.

Which graph shows the results of the investigation?