Technically, B isn't looking so great. The value range leaves something to be desired and it's a bit sloppy. The mouthpiece is probably the most interesting and finished part, otherwise this one needs work. I'd suggest the artist slow down on the blending (especially if it's with the fingers--BAD idea! use blending stumps) and focus more on establishing the value ranges. You should generally aim for at least 5 shades, from the brightest highlight to the darkest shadow and three middle range values. Here, there is predominately one, with slight highlights and hints of shadow.
C is pretty interesting. It looks more like an intaglio print than a drawing to me. Nice work with the hand and the shadow, but don't forget... the shadow is going to be darkest and the shape sharpest closest to the object casting it, that is, the fingers. The shadow should blur and lighten as it gets farther. It's too crisp. Also, don't forget with the arm the way shadows work. There is a slight highlight just after the darkest low-light. The curve of the arm is nice, but there should be a curve of the shadow with that highlight for it to look more realistic. The fingers could use more work, especially the thumb... it's a bit bulky. Otherwise, GREAT composition. The diagonals are really working well for the eye movement in this piece.
