Starting with your cylinders around arbitrary minor axes, I can see a great deal of improvement, especially when it comes to the underlying confidence of how you're executing your marks - and as a result, those later in the set definitely feel much stronger and more solid than those earlier on. It's not that the earlier ones aren't fine, it's more that it gives the impression that you weren't really sure of yourself, whereas the later ones seem ore certain.

On top of that, you've done a decent job of keeping an eye on the alignment of your ellipses' minor axes, although I did notice a few places where you may have perhaps been a little less attentive - like here where you drew your red analysis line roughly parallel with your intended minor axis, when the alignment was actually quite a ways off. Fortunately this didn't happen too often. It is however something you'll want to keep an eye on, as it wasn't so rare as to be a complete outlier.

Continuing onto the cylinders in boxes, your work here is by and large coming along quite well. There are two things that we must give each of our drawings throughout this course in order to get the most out of them. Those two things are space and time. Right now it appears that you are thinking ahead to how many drawings you'd like to fit on a given page. It certainly is admirable, as you clearly want to get more practice in, but in artificially limiting how much space you give a given drawing, you're limiting your brain's capacity for spatial reasoning, while also making it harder to engage your whole arm while drawing. The best approach to use here is to ensure that the first drawing on a given page is given as much room as it requires. Only when that drawing is done should we assess whether there is enough room for another. If there is, we should certainly add it, and reassess once again. If there isn't, it's perfectly okay to have just one drawing on a given page as long as it is making full use of the space available to it.

You have mostly done a good job of applying those line extensions so as to check how well your approach was performing, and to make adjustments to it as required from page to page - but, similarly to the issue with the minor axes I called out in regards to the first section of the challenge, there are places where this comes up here as well. It mostly comes down to the boxes that are extremely disproportionate, where they get squashed down in one dimension. As a result you end up with a very narrow ellipse, which can cause that minor axis to be so far off base that it appears to align towards one of your other vanishing points. As we can see here your minor axes end up aligning more closely with the green line extensions, instead of with the red. Remember - your minor axis needs to point down the length of the cylinder.

So, be sure to keep an eye on that. Fortunately, like the other issue, this didn't come up so often as to be a major problem, but also not so rarely as to not constitute a concern.

Aside from that, very nice work. I'll go ahead and mark this challenge as complete.