Starting with your cylinders around arbitrary minor axes, there is unfortunately a big issue with your work - but aside from that one unfortunately significant issue, everything else about your work here is excellent. You've been extremely mindful of investing as much time as is required into each mark, allocating that time to planning/preparation so as to still allow for a confident stroke, and have done a great job of checking your minor axis alignments, even as far as to catch fairly small discrepancies, which is important to avoid plateauing as we get into the "close enough" range.

The issue that you unfortunately did run into is that you didn't follow the instruction shown here in bold: to vary the rates of foreshortening from shallow (where there's very little noticeable convergence but not quite parallel on the page) to dramatic (where there's a lot of convergence over a short distance). This is an issue that in other situations I have assigned revisions for, but you're in luck - because the rest of your work is as well done as it is, I do not actually feel that this will require revisions to address. The mistake is pretty obvious, and I'm sure you'll pay closer attention to the instructions in the future.

Now, I do want to push one thing a bit further - because you were staying in the shallow end of the pool with these, you did end up with situations where some of your cylinders did not actually have any visible convergence, suggesting that the vanishing point may have been intentionally forced to infinity to simplify the problem. I do not actually believe this to be the case - rather, I think it was just that your intent was to add a little convergence but you flew a little too close to the sun, and it didn't end up coming through in the result. Still, I do think that I should explain why having those lines be parallel is incorrect.

We do not actually control where the vanishing points should be. Rather, we control how our edges in 3D space are oriented, and it is that which controls the location of the vanishing points. Specifically, a vanishing point would only go to infinity if the edges it governs run perpendicular to the angle at which the viewer looks out into the world - basically, where those edges do not slant towards or away from them through the depth of the scene. Since we're rotating our cylinders randomly throughout this challenge, the chances that they'd align so perfectly is small enough to be avoided altogether - so in the future, if you aren't fully intentionally aligning a set of edges that specifically, be sure to include some visible convergence, even if it's only very slight.

Continuing on, while I do feel that your cylinders in boxes initially started out with the same issue (trying to be too parallel, avoiding convergences/foreshortening/etc) you did catch this as you progressed through the set and started increasing the rate of foreshortening. As a result, you've largely done pretty well here, although I do think that you could stand to continue working on simple boxes (like from the box challenge, with line extensions) in your warmups if you haven't been already.

Ultimately, 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.

So, in applying that error checking correctly, you've given yourself ample opportunity to identify areas where your approach could be adjusted from page to page, and to generally hone that proportional instinct. While there is certainly plenty of room for continued growth in this area (since we've only done 100 of these), you should be in a good position to move onto the next lesson.

I'll go ahead and mark this challenge as complete.