Starting with your cylinders around arbitrary minor axes, overall you've done a pretty good job. I did notice a number of cases spread out throughout the set where you ended up making the side edges of your cylinders very parallel. In some cases like 123 it was definitely too parallel (in terms of contradicting what's stated here), while in others like 82 there may have been some desire to have those side edges converge, but it's hard to tell. In general though, since having them completely parallel on the page would be incorrect (again as explained in the section I linked), do try to always include some intentional convergence when drawing cylinders for this exercise.

Aside from those instances, you've done a great job - you've taken care with your linework, your ellipses are fairly evenly shaped, and you're mindful of checking all your minor axes and have caught both issues that were more noticeable, as well as those that are easier to miss, which should help you avoid plateauing in your practice.

Continuing onto your cylinders in boxes, by and large your work here is fairly well done, and you've taken care for the most part in applying your line extensions correctly. 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.

I do have one point that I want to call out, but before I do, I want to note that I only really saw this come up towards the beginning of this exercise, and you ironed it out pretty quickly. That just goes on to show that you are indeed internalizing and understanding the concepts put forward in this challenge - but I figured if I didn't mention it, I wouldn't be doing my job.

Basically the issue is that when your box gets very skinny in one dimension (and therefore very far from having squared ends), this can result in an ellipse with a minor axis that is way off from what we intend. While this in itself isn't an issue (since we should be catching that minor axis in our analysis), where it becomes a problem is that it becomes very easy to miss the fact that it's way off, and instead focus more on the general direction we want our minor axis to align. In other words, we end up identifying those minor axes incorrectly, or in the case that we might identify it correctly, we might mistakenly group it with one of the contact point lines, causing us to use a different colour. This in turn might make the significance of the mistake go unnoticed, since it wouldn't be, say, a single red line amidst several blues, but rather just another blue line with its colour chosen based on its direction, not its purpose.

So for example, here with box 164 I've identified the actual minor axis of these lines - they're very far off, although close to the green contact point lines in that direction so it's possible you could have gotten confused.

While as a whole this issue was only present towards the beginning, arguably what you stopped doing was constructing boxes that weren't suitable for this purpose - it's not that you necessarily caught the mistake itself in that you were misidentifying your minor axes, you just stopped putting yourself in a position to run into that problem. So, be sure to keep this in mind going forward.

Anyway, all in all, you're still doing very well. I'll go ahead and mark this challenge as complete.