In rembrandt van rijnâs the three crosses, how did the artist create a darkening landscape as the eye moves away from the crucified christ?

I believe the correct answer is by increasing the density of the lines.
If you take a look at the painting I've attached, you will see that the lines are quite thin in the middle where Jesus is crucified. However, as your eye moves away from Christ, you will see that the lines become thicker and thicker until they become completely black on the sides of the painting. 

Iwould say d) signed unknown street singers who brought original songs to record.