Answer:
The phrase that best contributes to the author's sad tone in this excerpt is D: silent sterile shores.
Explanation:
This line has the job of expressing how dead Lake Powell looks like to the author, how it makes him/her feel. The words chosen to describe the sensation Lake Powell gives make a very good job in transmitting the reader the sad vibe you feel when you look at this place. Especially, the words silent and sterile give a bad connotation and a sad tone to the excerpt.
