Line>Shape

I think that they could all be lines or shapes. Lines are generally open marks that can range as anything from a mark showing the distance from point A to point B, or they could be deep squiggles all over the paper. They also tend to show a lot more movement then a shape, as shapes are solid and "stay in one place." A line easily becomes a shape simply by connecting one end of a line to the other.
I see Image A as more of a closed, geometric shape (like a wedge) rather then a open line. B could be part of a cursive V which would be more line-like then shape like. C looks like a rectangle, but could also be a linear dash, but appears to be too thick to be just a line. D is very organic, like a plant, but could be just a "squiggle-line," with a lot of movement and speed to it. I think part of what makes me think of shapes instead of lines with these is because they're filled in with black, making the postive space so much more noticeable. With a line, the negative, bright space stands out more.