Starting with the cylinders around arbitrary minor axes, your work here is for the most part quite well done, with one issue I want to call out. Before we get to that however, your linework is generally pretty solid - confident, straight lines, and a lot of smooth, even ellipses. Some of them get a touch uneven or loose, but they seem to be blips whereas the main trend shows care and preparation prior to a confident execution. I'm also pleased to see that you're quite fastidious in analyzing your ellipses and finding their 'true' minor axis/orientation.

So the issue I wanted to talk about was that, while this definitely diminishes throughout the set, towards the beginning and here and there towards the end, you were drawing cylinders with no foreshortening whatsoever. That is to say, the side edges of the cylinders were drawn to remain parallel on the page, rather than converging towards a vanishing point.

So for example, we can see this on cylinder 143, though there are many others. Foreshortening manifests in two ways - one through the shift in degree from one end of the cylinder to the other, as well as through the shift in scale, where the far end is smaller overall than the closer end because of the way in which the side edges converge rather than remaining parallel on the page. These two signs of foreshortening should remain consistent - either a more dramatic shift in both, or a shallower shift in both, but not one shallow and one dramatic, to avoid a contradiction.

The foreshortening itself represents how much of the form's length exists in the "unseen" dimension of depth - which can't be represented by a simple distance across a flat piece of paper. Instead, the viewer's brain looks at the length they can see, and multiplies it by how much foreshortening there is being applied to the form, to better understand its relative length in 3D space. If however we provide no foreshortening whatsoever, then we're telling the viewer that the length they can see should be multipled by 0 - and therefore that there is no length, which leads to a direct contradiction with at least part of what they can see.

Continuing onto your cylinders in boxes, overall you've done a good job here, with one little issue that may have hindered your progress a little. From what I can see, you've done a great job of applying the line extensions in most cases (although I did notice that on number 1 you accidentally extended one of the sets towards the viewer instead of away, but since it was a one-off thing, it's not a big deal). When extending your minor axis lines however, you seemed to confuse it with the way in which we checked our minor axes in the previous exercise. Here, it's important that you extend those minor axis lines as far as all the others.

Reason being, the focus of this exercise is to help students develop a more instinctual grasp of how to draw boxes that feature two opposite faces which are roughly proportionally square. We do this by taking the line extensions from the box challenge, which through iteration would gradually attune students' brains to drawing edges that converge consistently, and we add the cylinder - or more specifically, the two ellipses and the 3 lines they each bring: the minor axis, and the two contact point lines.

Should those lines converge towards the box's own vanishing points (minor axes towards the same VP as the cylinder's side edges, and the contact point lines each towards one of the other VPs), then we know that the ellipse itself represents a circle in 3D space - and therefore the plane enclosing it would represent a square in 3D space. Of course, we're only human, and won't achieve such perfection without a ton of practice, so instead analyzing where we're off and by how much, we can make small adjustments to bring things back in line.

If however we don't extend those minor axis lines as far as the others, it becomes easier to overlook areas where they may be off. It's not such a huge deal here - you were checking them after all - but it is definitely something to be aware of when doing this exercise in the future.

Anyway, all in all, your work is coming along well, and while I've given you a couple things to keep an eye on, you can consider this challenge complete.