Look at which way each crescent faces and at its colour. One rule works along the rows and another down the columns. Which crescent is missing?

Along every row the crescent turns a quarter turn anticlockwise: in the top row its curved back faces right, then up, then left. Down every column the colour stays the same: orange, blue, yellow. In the bottom row the back faces left and then down, so in the last cell it faces right, and the crescent is yellow: (b). (a) turns the wrong way, (c) has the colour of the middle column and (d) has not turned.