Aristotle says that a plot should have a clear beginning, middle, and end and should feel unified. this is another way of saying

a. that a plot should follow logically from start to finish and feel like everything that happens is necessary
b. that a plot should be fun and exciting, even at the expense of logic
c. that a plot should follow cause and effect and not use songs unless it is a musical
d. that dramatic unity is not a substitute for the logical progression of a story's events