Only one of these shapes of six squares is the net of a cube. Which one?

(c) has a column of three with one square on each side and one more below: it folds into a cube. (a) has two rows of three overlapping by two squares, so two faces land on the same side. (b) has five squares in a line, more than a ring of four. (d) has squares standing above both ends of its row of three; both fold up onto the same face.