Last critique of the day! Jumping right in with your cylinders around arbitrary minor axes, you've done a great job here. Your ellipses are drawn confidently, maintaining even and smooth shapes, and your linework as a whole shows good, consistent use of the ghosting method. You've also done a great job of checking those minor axes quite fastidiously - it's honestly less important to me that every single one be absolutely perfect (as you were asking about in regards to the boxed cylinders), and more that students don't fall into the trap of being like "ohhh that's so close, so I'm just going to draw my red line so it follows the original minor axis I drew". Rather, it's preferable to see students marking out even those smaller discrepancies, as it does show that they're thinking about it a great deal.

On top of that, I'm pleased to see that you played with a decent amount of foreshortening here. Admittedly most of these have a middling amount of foreshortening, though you do have some that are shallower (but not perfectly parallel on the page, as that'd be a mistake), and some that are more dramatic. I can also see that you appear to be aware (whether consciously or subconsciously) of how the two shifts of the ellipses from one end to the other (the scale shift which makes the far end get smaller overall, and the degree shift which makes the far end wider) operate in tandem (in other words, at the same rate). This is important, as both of these are manifestations of foreshortening, and tell the viewer whether the cylinder they're looking at is, in 3D space, about as long as what they see in the page (in the case of shallower foreshortening, or a more gradual, minimal shift from one end to the other), or whether the bulk of its length exists in the "unseen" dimension of depth.

If however we have a more dramatic scale shift, with the far end being much smaller, but a subtler, more gradual shift in degree, with the far end being only slightly wider than the closer end, then the viewer would be getting mixed signals. They might not be able to pinpoint what the problem is, but it would look "off" to them.

But again - you avoided that, so good job. If it was instinctual rather than conscious, then my explanation will hopefully have pushed it into a more solid understanding of the mechanics behind all this.

Continuing onto your cylinders in boxes, you've done a good job here as well. While I'm sure you've probably read this, or been told this already, it's pretty much all I have to talk about in this challenge - 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.

Throughout your work here, you've done a great job of identifying those line extensions correctly, picking up both subtle and really dramatic mistakes, and as a result, you have certainly pushed towards a more solid grasp of how to apply these proportions regardless of how specifically the boxes are oriented in space. There's certainly still room for improvement here, but as a whole I think what you've developed here already will serve you well into lesson 6.

So! I'll go ahead and mark this challenge as complete. Keep up the great work.