Chris is preparing for a comprehensive course exam by reading a textbook with chapters of equal length and difficulty. The number of chapters she can comprehend and master when studying is: (1) hour one: 1.5 chapters; (2) hour two: 2.0 chapters; (3) hour three: 1.5 chapters; (4) hour four: 1 chapter; (5) hour five: 0 chapters. Diminishing marginal returns to studying sets in for Chris after hour: