Starting with the cylinders drawn around central minor axes, there's definitely a lot of great stuff here. Your ellipses are confidently drawn, your linework is precise and accurate (without any wobbles or hesitation), and you've been very fastidious in checking the true alignment of your minor axes.

There is one issue that comes up now and then - while many of your cylinders do have some subtle foreshortening to them, there are a number of them (like 146, 106, 82, 68, 27, 19, and many more towards the beginning) that appear to maintain entirely parallel side edges, effectively putting their respective vanishing point "at infinity" (in the manner discussed back in Lesson 1). This is actually incorrect. The only situation in which a vanishing point would actually "go to infinity" is if the set of edges it governs actually run perpendicular to the viewer's angle of sight, not slanting towards or away from the viewer through the depth of the scene. Given that we're working with randomly rotated forms in this challenge, we can pretty much trust that they'd never align so perfectly.

Furthermore, it's worth talking about foreshortening in general. Foreshortening manifests in these cylinders through the shift in scale from one end to the other caused by that convergence (so the closer end is bigger, farther end is smaller), as well as the shift in degree between ellipses (closer end narrower, farther end wider). These two shifts happen in tandem, for the most part, so if there's a more dramatic shift in degree, there should also be a more dramatic shift in scale, and vice versa. Just something to keep in mind.

In general that's an issue I look for in students' work, and it's the reason I ask for students to include a lot of variety in their rates of foreshortening in the assignment section. I didn't notice the issue too significantly (except when the vanishing points were artificially placed at infinity), but I figured I'd explain the concept anyway since you didn't really delve into particularly dramatic foreshortening all that much.

Continuing onto your cylinders in boxes, here you have done very 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.

You've been very careful and patient in applying those line extensions, and in learning from them, and I can see your estimation of those proportions developing nicely throughout the set. This should come in quite handy as you move onto lesson 6.

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