In order to transform from ABCD into A'B'C'D', we can see that the orientation is different, therefore we need a rotation.
Looking at the coordinates, the x and y coordinates of every point were swapped, and the signal was reajusted so all coordinates are positive (since the figure is in the 1st quadrant), so that means we had a rotation over the origin.
The original figure is in the 2nd quadrant and the new figure is in the 1st one, so the rotation is 90° clockwise (or 270° counterclockwise).
Therefore the correct option is A.