Each net has two red, two blue and two yellow squares. For which net does every face of the folded cube have the same colour as the face opposite it?

(b) is a staircase, where squares two steps apart are opposite: red–red, blue–blue and yellow–yellow. In (a) the ends of each row are opposite, giving red–yellow twice; in (c) yellow is opposite blue; in (d) red is opposite blue.