Answer:
Allusion is the answer. It's mentioning the river and what it's known for but not telling you the name of the river.
The correct answer is plot. Theme is the work's main idea (the "why" of the work), and there usually are more themes in a single work. Narrator is the "I" of the story, someone who tells it. The setting is the "when and where" of the story, the time-place frame. The plot is the "what" - what happens.
It is independent because it expresses a complete tought.
A. Helping verb, it describes the subject as it renames.
