Some students investigated the effect of pH on the rate of starch digestion by amylase at 20 °C. • They added 2 cm³ of a 1% amylase solution and 1 cm³ of pH 4 buffer to a test-tube. • They added 2 cm³ of a starch solution, containing 0.02 g of starch, to the test-tube. • They measured the time taken for the starch to be digested (to disappear). The students then repeated these steps with pH 5, pH 6, pH 7 and pH 8 buffers. The table shows the results. [Table with columns 'pH' and 'time taken for starch to be digested / minutes' and rows 4: 4.0, 5: 1.5, 6: 1.0, 7: 2.5, 8: 6.0] Which graph is correct for these data?

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