The plot of A's novel was full of ups and downs, and its cadence was very infectious. cadence: To describe the ups and downs of a voice and the changes in cadence. Ups and downs: To describe the plot's twists and turns and dramatic changes. The word "cadence" in this sentence was used to describe the plot of the novel, which was full of ups and downs and dramatic. The word "ups and downs" was more suitable to describe the plot of the novel, which was full of ups and downs and changes. Therefore, the appropriate word to use was "cadence".