Alrighty! So all in all, you're doing a pretty good job. You've been fastidious in applying your minor axis corrections and your line extensions, and you've shown a good deal of improvement over the whole set. There are a couple things I'd like to point out which should help both give this challenge a greater sense of context and purpose, and that should also help you as you move forwards.

First off, your cylinders around arbitrary minor axis are quite well done. Your ellipses maintain nice, even shapes, and you've identified even slight discrepancies in their alignments. I am noticing a slight tendency to be just a little timid when drawing your ellipses - where we can see your pen "skip" (causing small gaps in the lines). While your results are still fine, it does suggest that you may be drawing just a little more lightly. This can often cause students to hesitate more, because they're balancing both how heavily they make their mark and all the other factors that go into drawing a proper ellipse. I'm pleased that you're managing it all fairly well, but generally I do discourage students from getting too caught up in drawing with too light a touch.

One thing I try to give students the opportunity to figure out themselves is the relationship between foreshortening and the shift in the degree of our ellipses. Now, we already understand that the shift in scale from the near end to the far end is a hallmark of foreshortening, and basically tells the viewer whether there is a small distance or a larger distance between those ends (basically whether the cylinder is long or short). Now, most of your cylinders are pretty shallow with their foreshortening, so there wasn't a lot of opportunity to explore this - but I did notice a couple cases, like #137 to help illustrate this point.

Just like the shift in scale is a part of foreshortening, so too is the shift in degree. When that shift is more dramatic (if the far end gets much wider than the closer end), it also tells us that the cylinder is longer.

If we compare 137 and 142, we'll see that 137 looks just slightly off. The reason for this is that it has a contradiction. It's got a slightly more significant scale shift (the far end is more notably smaller than the near end), but very little shift in degree. 142 on the other hand has a little more of a shift in its degree, better to match the shift in scale. Long story short, 137 is incorrect because the scale shift says it's longer, whereas the degree shift says it's shorter.

Similarly, if there were a case where the degree shift were dramatic and the scale shift were minimal, it would also be contradictory. Definitely something useful to keep in mind, as this principle actually applies to all forms - even boxes will have a far end that steadily gets proportionally wider (while still getting smaller overall) as the box gets longer in that dimension.

Moving onto your cylinders in boxes, there's one issue I wanted to highlight, and it's a pretty simple one - your linework gets erratic. You tend a lot more towards correcting mistakes, and automatically reinforcing lines instead of executing each stroke with the patience and control of the ghosting method. This isn't always the case, sometimes you reel yourself in and get back in line, but you still do show a bad habit of going back over lines you shouldn't be. To put it simply, you need to discipline yourself - if you make a mistake, no big deal. They happen. Don't go back over it, because you'll just add more ink, drawing more attention to the problem.

Now, the thing about the cylinders in boxes exercise is that it is fundamentally more about the boxes than it is about the cylinders. Specifically, it trains students to get better and better at constructing boxes that have two opposite faces that are proportionally square. Just like how we add line extensions to our box challenge boxes to get better at identifying mistakes, and then eliminating mistakes in terms of whether or not those lines converge consistently, here we add the cylinder to identify where our planes are not quite proportionally square. As we get better at the challenge, we get better at constructing these proportionally square faces intuitively, against a set of implied vanishing points.

To this end, you've larlgey improved quite a bit, and by the end there are very few cases where the ends feel obviously squished.

So! All in all, nice work. I'll go ahead and mark this challenge as complete.