Starting with your cylinders around arbitrary minor axes, there are some issues, but as far as the exercise itself is concerned, you've done well, and I can see improvement over the course of the set. You've been quite fastidious in checking the alignment of your ellipses, and you've done a good job of varying the rate of foreshortening across the set. I can also see that, while you may not be entirely consciously aware of the reasoning behind this, that you've naturally increased the degree of your far end, as the scale of that far end increases. Basically, both of these shifts (the degree shift and the scale shift) are signs that help us understand how much foreshortening is being applied to the form - that is, how much of its length exists right on the page, and how much exists in the "unseen" dimension of depth. These of course have to work in tandem.

This is something I don't mention ahead of time, but I look for it when giving critique. Reason being, students who pick up on this on their own (as you appear to have done so, even if you weren't fully conscious of it) will retain the conceptual understanding more strongly, with an explanation merely helping to solidify what their instincts already told them.

Now, there is one big issue with your cylinders in this section - it's the fact that your ellipses are pretty uneven. They do get better over the course of the set, but it appears to me that you're not applying the ghosting method to your linework (I'm not seeing the usual signs that you're using it for the side edges either, though they're generally pretty smooth, so at least you're executing them with confidence). In addition to this, the unevenness of your ellipses also suggests that you are not executing them using your whole arm from the shoulder, and that you may be slipping back to your elbow or your wrist.

While it is not at all uncommon for students to still have a rough time with ellipses at this point (after this point we allow for the use of tools like ellipse guides so that they don't distract students from the core focus of the later lessons, which are quite involved), this does suggest to me that you may not have been practicing your ellipses/use of the ghosting method/use of your whole arm from the shoulder in your warmups. Ultimately I will have to leave this to you to address yourself however, as the course has provided all of the exercises you need to improve on this front - you just have to keep up with it.

Continuing onto the cylinders in boxes, here you've done quite well. This exercise is really all about helping develop students' understanding of how to construct boxes which feature two opposite faces which are proportionally square, regardless of how the form is oriented in space. We do this not by memorizing every possible configuration, but rather by continuing to develop your subconscious understanding of space through repetition, and through analysis (by way of the line extensions).

Where the box challenge's line extensions helped to develop a stronger sense of how to achieve more consistent convergences in our lines, here we add three more lines for each ellipse: the minor axis, and the two contact point lines. In checking how far off these are from converging towards the box's own vanishing points, we can see how far off we were from having the ellipse represent a circle in 3D space, and in turn how far off we were from having the plane that encloses it from representing a square.

In applying the line extensions fastidiously across the whole set, you've been able to gradually train the way in which your brain understands those proportions, helping you to get a better instinctual sense of what proportions to use depending on the given orientation of the form. This should help you a great deal as you continue on from there.

So, I'll go ahead and mark this challenge as complete. Just be sure to keep up with your ellipses in your warmups, and be sure to engage your whole arm from the shoulder.