This, is just amazingly realistic. It's nice to see that every body has some variation, even though its clear that you like to draw, like, what you like.
The shading is done wery well, and the blending with the backround looks nice. The white on the skin looks like a reflection, not just a blank space.
The anatomy of the bodies themselves looks very neat, and I cant spot any majos flaws. The only thing is that you could have taken this a step foward, and drawn clearly different body types. Overrall, this is an excellent and very realistic sketch