Answer:
-We are as clouds that veil the midnight moon;
How restlessly they speed, and gleam, and quive
Step-by-step explanation:
In these lines, Shelley compares people to clouds that appear at night and veil the midnight moon. He states that these clouds "speed, gleam and quiver" restlessly. The metaphor is intended to reference human life. Just like the clouds, human life is brief. Therefore, these are the lines that best support the idea that life is fleeting.