Jumping right into your cylinders with arbitrary minor axes, one thing stands out above all the rest - it appears that for the vast majority of these cylinders (aside from about 16 - I know this because I counted), you have drawn them such that the side edges do not converge at all towards a shared vanishing point. There are two issues with this.

Firstly, it means that you didn't really vary your rates of foreshortening much (among the 16, there were a few that were more dramatic in foreshortening, but still others that were still quite shallow). Note that as shown here the assignment section does specifically request that students vary the rate of their foreshortening.

This would be less of a concern if the vast majority of your cylinders had been of shallow foreshortening, but what you've done here is actually eliminate the foreshortening altogether, forcing that vanishing point "to infinity" (a concept discussed back in Lesson 1). The thing is, it's not just a choice being made that was contrary to what was requested - it's actually incorrect.

It's incorrect because we cannot force our vanishing point to be anywhere in this manner. Rather, we control the orientation in which we wish to draw the given form, and thus the orientation of the various sets of parallel edges that make it up in 3D space. It's these orientations which in turn determine where the vanishing points would go, and more importantly, there is only one limited set of circumstances in which a vanishing point would go to infinity: if the set of edges it governs in 3D space run perpendicular to the viewer's angle of sight, not slanting towards or away from them through the depth of the scene.

Also, given that the cylinders we're drawing here are totally randomly rotated (like the box challenge), we can pretty much say that the chances of any of our cylinders in a sample size if 150 aligning so perfectly is slim enough that we may as well assume it won't happen. Thus, we work with concrete vanishing points and convergences, even if they're only very gradual.

Normally in a situation like this, I'd assign significant revisions, but there are a lot of factors that go into that decision, and t he presence of those 16 other cylinders - all of which were generally pretty well done - does make that decision a bit harder to make. So, I decided that if your cylinders in boxes were done well, I'd let you continue on without revisions, and if not, I'd assign a full revision.

Your cylinders in boxes started out kind of rough at first, but they improved quickly, and it's clear that throughout (even at the very beginning) you were trying to apply the principles behind the line extensions, and you were doing so well. As you progressed through it, you held to this and ultimately you did a great job.

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 holding to those line extensions conscientiously and consistently, you were able to identify issues and address them by shifting your approach from page to page, and so by the end you're actually in a pretty strong position when it comes to estimating the correct proportions for your boxes, regardless of how it's meant to be oriented in space.

So, as promised, I'll go ahead and mark this challenge as complete. Just keep what I said about foreshortening and parallel lines in mind as you move forwards, and be sure to continue practicing these kinds of exercises as part of your regular warmups.