Overall you've done a pretty good job with this challenge. You've been mindful of keeping your ellipses fairly evenly shaped by drawing them more confidently, and throughout the two sections you've been conscientious with your corrections (identifying the correct minor axes, doing your line extensions, and so on).

Starting with your cylinders around arbitrary minor axes, one thing I do want to draw your attention to is something that wasn't explicitly stated elsewhere, but something I wanted to give students an opportunity to discover on their own. Basically, it's about the relationship between the shift in scale from one end to the other (where the far end gets smaller overall), and the shift in degree from one end to the other (where the farther end is of a wider degree than the closer end). What you may not have picked up on entirely is that both of these are facets of foreshortening - meaning that they both convey to the viewer whether the farther end of the ellipse is fairly close to the other end, or whether it's very far away (basically whether the cylinder is long or short).

Since they both relate to how long the cylinder is, there are certain circumstances that aren't going to occur. What you shouldn't ever see are situations like cylinder 130 where the far end is considerably wider than the near end (suggesting a longer cylinder), but the far end is also fairly close in overall scale (which suggests a shorter cylinder). You're going to have either a dramatic shift of both scale and degree (a lot wider and a lot smaller) or a minimal shift (only a little wider/smaller), not both.

Looking at your work, scale shift is something you didn't really play with much, and in the future I'd definitely recommend doing that more.

Moving onto the cylinders in boxes, the actual purpose for this exercise isn't really about learning how to draw cylinders in boxes. The core is actually about learning how to draw boxes that have a pair opposite faces which are proportionally square. Just like how the line extensions from the box challenge help us identify where your sets of parallel lines do not consistently converge towards a shared vanishing point, the cylinder is essentially an extension of that. If the plane we've drawn is not actually a square in 3D space (relative to the various vanishing points), then the ellipse we draw within it won't have a minor axis or contact points that align with all of the other line extensions. So, as we continue to work on getting those minor axes and contact points to align better, we steadily build on our ability to draw those boxes such that the planes are actually square, and therefore the ellipses they contain are actually circles in 3D space.

To this end, I feel you've shown a good deal of progress, and your comfort with drawing boxes with pairs of faces that are proportionally square has definitely improved over the set.

All in all, your work here is looking great - just be sure to play more with foreshortening in that first section. I'll go ahead and mark this challenge as complete.