Starting with your cylinders around arbitrary minor axes, your work here is by and large well done, but there are a couple considerations I want to share with you. In general however, you're doing a good job of drawing your ellipses with confidence, you're maintaining smooth, consistent, straight edges, and your error checking appears to be mindful of capturing even small misalignments, so you can keep on top of the little issues as your skills get to the point that is likely to result in plateauing and stalling.

Now, the first point I want to address are the cases where the side edges of your cylinders get a little too parallel, where they fall into appearing as though your intent was not to have them converge, but rather to force the vanishing point governing them to "infinity" as discussed in Lesson 1. We can see this in cases like this on the page marked "105", and here on the page marked 5, and many other occasions in between. The reason these are concerns is that in this challenge we're effectively rotating our cylinders at entirely random orientations, but a vanishing point only goes to infinity when the edges it governs in 3D space run perpendicular to he angle at which the viewer is looking out into the world. We don't actually control the position of the vanishing point - just the intended orientation of the form, which dictates the vanishing point.

Given that random rotation we're going for, we're much safer simply assuming that the alignment will never be so perfect, and thus the edges will always have some convergence to them. There are a lot of other cases, like this one where your cylinders appear to be fairly parallel on the sides, but there's enough convergence to keep you from falling into this issue. I'd recommend using that as your general "minimum" amount of convergence.

The other point I wanted to talk about is to keep in mind that the degree of your ellipses conveys the orientation of each of those circles in 3D space, and consider how this might work in tandem with how the cylinder as a whole is being drawn. So for example, here (from the page marked 100) you've got some fairly wide ellipses, suggesting that they aren't entirely facing the viewer head-on, but they are pretty close to it. This means that the distance on the page between the ellipses is suggesting a rather extreme length for the cylinder, given that the cylinder is oriented more towards the viewer, and that most of its physical length therefore exists in the "unseen" dimension of depth.

For cylinder with a more reasonable length, you're more likely to have the ellipses being closer together, and even overlapping one another a little. Conversely, if the intent was to have an extremely long cylinder, then that would suggest that the far end is very far away from the viewer - meaning it should be represented with a much smaller ellipse.

So! Just be sure to keep these points in mind when drawing your cylinders.

Continuing onto your cylinders in boxes, fortunately there isn't too much to say here, as you've done a solid 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 applying the line extensions correctly - and even catching cases that were wildly off base like this one from the page labelled 239 - you've done a good job of building up your instinctual awareness of the proportions of your boxes, allowing you to pretty consistently nail them closely enough for the naked eye. This should come in quite handy throughout the next lesson.

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