like the expression on E! :D

The face structure is certainly interesting, like how on "C" the jaw line has a more structured look and is less 'squishy', like the jaw of a steriotypical action hero. It's a good way of making a character appear 'cool' and in control. As opposed to most of the other ones that have the aformentioned 'squishyness' that makes it more cartoony and charismatic. Though "B" for some reason looks a little realistic, I mean, anatomically correct. And "E" for some reason looks like his muzzle is a big nose hanging down in front of his face, which is the only thing that I can say I don't actually like. The rest are fun and very good artistic exercises.

What are you doing in D :)
Grand expressions there.