Starting with your cylinders around arbitrary minor axes, you've done a pretty good job here, and I'm definitely seeing a fair bit of improvement over the course of the set. That improvement may not necessarily be entirely apparent (as it's not necessarily something everyone's attuned to noticing), but I can see quite clearly that the confidence behind your linework - both the straight edges along the sides of your cylinders and the ellipses at either end - noticeably improves. I'm also pleased to see that you're consistently checking your ellipse alignment throughout the set, catching even relatively small deviations. This is important as it helps us avoid plateauing, when we get into that territory where to the naked eye, everything looks fine.

The one thing that I would stress however is that when you practice this on your own in the future, be sure to vary your cylinders - not just the length (you did indeed make most of them quite long) but also in terms of the orientation. That takes into consideration both the degree of the ellipses themselves (they'd generally be quite a bit wider, due to those circles in 3D space pointing the viewer head-on), as well as how close together the ellipses are (since when the cylinders' facing us head on, it means more of its length exists in the unseen dimension of depth, with far less of it being directly present on the page).

Continuing onto your cylinders in boxes, there's one overarching issue that I do want to mention, but setting that aside, you are handling the exercise quite 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.

As far as that is concerned, you're doing really well - but what you're missing (or at least what you appear to be missing) is that a lot of your boxes, especially the longer ones, tend to have their lines converging in pairs, instead of having all 4 converge together. So to illustrate the point, here I've marked out all the points to which your edges converge. The ones I've circled should of course just be a single vanishing point each, but right now instead of having 3 vanishing points, you've got 5. This means that the ends of the cylinder/box are not parallel to one another, as they should be.

This is something you do less later on in the set, with it being considerably more frequent earlier on, but given that it's still quite noticeable, it is something you'll want to work at as you continue moving forwards.

So! Keep that in mind, and I'll go ahead and mark this challenge as complete.