Things can always be done better - but that's not really what matters. It's a question of whether or not it has been done to the best of our current ability, and whether work that has been done to that standard reflects an understanding of the concepts covered in the lesson. In many regards, I feel that your work does, though there certainly are some issues that I would like to point out.

To start, I think overall you're demonstrating a good deal of improvement over the set, and that your understanding of how to employ additional masses to bulk out a structure in seemingly arbitrary ways to capture elements of the specific reference you're studying develops quite a bit. At the beginning your constructions feel more as though they're built up with individual shapes layered on top of one another. In some areas we can strain our brains to perceive a relationship between them, but it certainly isn't given to us freely, and it is quite easy to just understand the drawing as a series of shapes on a page.

This continues from the birds and into the sitting bear - though I can see areas of the sitting bear where you're trying to sort out just how those masses actually start to wrap around the underlying structure. I mostly see this on the masses used at the neck, where you're starting to consider how they curve around the structure that is present.

It's your next few bears where this starts to solidify - though there are still some issues. The relationship between the forms still isn't totally solid however - for example, the mass along the rump of the top bear still feels as though it's just sitting gently atop the structure rather than really clinging to it. Also, when adding masses to the legs you're still largely just pasting on simple shapes. That said, there is improvement in the bottom one especially when it comes to adding to its torso.

As shown here, you really need to exaggerate just how those forms wrap around whatever structure already exists - be it the basic masses of the construction, or other additional masses that have been added thus far. Your new form needs to run along the surface and really cling to it. I also point out there how you have a tendency to draw your eye sockets too small. The face is a 3D puzzle with pieces that fit snugly into one another - you'll find that the eye socket can be drawn much larger, and it'll be buttressed by the muzzle, the brow ridge and the cheekbone.

I do see signs that you're using the sausage method, though in the bears you weren't adhering to it quite as closely as you ought to - so just for the sake of completeness, be sure to review the major steps of the technique. That is, constructing the segments out of simple sausage forms (two equally sized spheres connected by a tube of consistent width), make sure they're interpenetrating properly, and then reinforce the joint with a contour curve that defines the relationship between the two sausages. As I mentioned before, you do a good job of this through much of the lesson, but I just wanted to lay out that out for the few cases where you got a little lax.

Once you've got your sausage-leg laid down, additional masses needed to bulk it out (as shown above) need to wrap around the new structure, as shown here.

The last thing I wanted to talk about was how you draw your fur. You generally draw it as fairly similar individual spikes. You tend to have at least one line of these spikes penetrating deeper into the silhouette of the object. In doing this, you're emphasizing the fact that each of these spikes are just individual lines, and not really giving the impression that you're actually breaking up the silhouette of the object. If you look at the diagram here and focus just on the ones that build up along the silhouette (forget about all the internal lines), you'll see that I'm effectively designing very specific clumps of fur that extend the silhouette's shape. I'm taking the outline of that ball and changing its path, resulting in a single shape, not a series of additions on top of the shape as it was previously. At the end of the day I still want it to read as just being the silhouette of the same form as before (merely altered), rather than a bunch of separate lines stamped together.

As I said at the beginning, you're doing a pretty good job, and are making good headway. I do however want to push you on the issues I've called out here, and see if you're able to apply them a little better. As such, I'll be asking for a few additional pages which I'll list below.