The sentence should be "By nightfall, they <span>will have been driving</span> for ten hours" since this is perfect in the sense that it WILL have happened in the past by the time it happens.
Answer: It shows the types of things that drones fly through in races.
Some might experience per say an emotional high and low. Colors can also have a play in this. Usually a sunset goes up with soft colors but when the sunset starts to go away, all is lost and more harsher colors come into context. As in with the more softer colors, you feel relaxed and carefree. Wit the harsher colors, you feel angry and sad.
