Final answer:
D.slim valley Save and Exit Submit Mark this and return​. The words "slim valley" in the paragraph are the best context clues for understanding the meaning of the underlined word, which indicates a narrow gorge.
Step-by-step explanation:
In the given paragraph, the words that best help readers to find the meaning of the underlined word, which refers to a narrow valley, are "slim valley." The context clues provided by these words allow readers to infer that the gorge mentioned is a narrow space, much like that of a slender or slim valley. This connection helps readers understand that the underlined word, in this case, denotes a narrow passage between two larger landforms, giving a sense of both the shape and spatial qualities of the gorge.