答案：D

解析：

The word "so" indicates that the sentence is a cause-and-effect statement: the second half of the sentence must describe the way readers must respond to a novel that "consists of discrete vignettes." Inserting the terms in choice (D) into the sentence creates a logical cause-and-effect statement. If the novel is composed of "discrete," or unconnected, episodes, then the reader must supply the "connections" that bind these apparently "independent" parts.