Actually. Now that I look again, I don't think it can be A or B. C is still definitely out.
I don't think A or B works, because if the base were a square, I think that means the cylindrical object coming out of it would have to be raised up on the square base. How do you have a cylinder rise up from a square base without there being an edge? If it were a square base, I think you'd see an edge on the front and end views along the bottom of the figure. So I think that's why it's D.
But that's really annoying, and mean. Haha.