Very nice work overall. Starting with your cylinders around arbitrary minor axes, you're doing a great job of drawing your ellipses with a good deal of control and accuracy, while maintaining their confident, even shapes. You're also clearly putting a lot of time into analyzing the orientation of those ellipses afterwards, properly identifying their "true" minor axes, and improving upon them page after page.

I'm also pleased to see that there is some variety in the foreshortening on your cylinders - there could definitely be more, but really the main thing I'm worried about is students who completely skip foreshortening altogether, trying to keep the edges of their cylinders arbitrarily parallel. Doing so would be incorrect, so I'm very glad to see that even when you keep your foreshortening fairly shallow, you're still mindful of the far off vanishing point and the edges' convergence towards it.

There's just one small thing I want you to keep in mind move forwards - though it's possible you are already aware of this. Looking at cylinder 70, there's an example of a common mistake that students make. Because there aren't really any cases of particularly dramatic foreshortening in your set, it's kind of hard to gauge whether you do in fact understand this, so I'm going to go ahead and explain it anyway.

All of your cylinders feature two "shifts" as we move from one ellipse to the other. One is the shift in scale, where the closer one is larger overall, and the farther one is smaller. The other shift is in degree - the farther one is proportionally wider, and the closer one is narrower.

If you look at cylinder 70, you'll note that the scale shift is more notable, but the degree shift is fairly minimal. Both shifts are manifestations of foreshortening, which means that they help the viewer determine just how much of the cylinder's length is unseen (occuring in the dimension of depth, which we can't see on this flat page), and how much is more visible due to moving across the picture plane. Based on the scale shift, we can see that there is a more significant amount of the cylinder's length that is "hidden" - but based on the degree shift, there's actually only a little bit that is hidden. This leads to a visual contradiction - either the cylinder's got something to hide, or it doesn't.

Basically, you want to make sure that the two signs of foreshortening are roughly consistent with one another - if you've got a more dramatic shift in scale, you should also feature a more dramatic shift in degree, and vice versa. If one is more gradual and shallow, the other one should match.

Now across most of your cylinders, you include this as a matter of course, with a minor shift in both areas, but I wanted to be sure that this was intentional, and if not, that you understood the concept.

Continuing onto your cylinders in boxes, your work here for the most part is really well done, with one small suggestion. This exercise basically focuses on the boxes themselves - training students to develop a more intuitive grasp of their proportions, and how to construct boxes that feature two opposite faces which are roughly square.

We do this by including the cylinder as part of the error checking section - just as the box challenge has the line extensions which help us improve the consistency of our convergences, here we add lines for each ellipse that allow us to test whether those ellipses represent circles in 3D space, and whether the planes enclosing them are in fact squares in 3D space.

As far as this is concerned, you're doing a great job, and are progressing nicely. One thing that will help you continue to progress in this direction however is to extend your minor axis lines (which appear to be among the yellow lines) further, so you can better test their relationship with the box's own vanishing points. Right now you're extending them more similarly to the first section (so the end closer to the viewer ends up extended towards them). This is great for checking their individual orientation, but ends up lacking somewhat when it comes to analyzing their relationship with the box's VPs.

Anyway, all in all, great work. I'll go ahead and mark this challenge as complete.