For serine, pKalpha-COOH = 2.21, and for leucine, pKalpha-COOH = 2.36. If a mixture of 10 millimoles each of serine and leucine at pH = 2.40 is passed through a cation-exchange column and eluted with additional buffer at pH = 2.40, which of the following will take place? A. Serine and leucine will elute together. B. Neither serine nor leucine are eluted from the column because the pH of the elution buffer is too low. C. Neither serine nor leucine are eluted from the column because the pH of the elution buffer is too high. D. Leucine will elute first, followed by serine. E. Serine will elute first, followed by leucine.