A $4\times 4$ grid has three dots, one yellow square and one red half-square. Which panel shows the grid in the dashed mirror?

Each mark moves to the same row but the opposite column: the top-left dot goes to the top-right, the yellow square from column 2 to column 3, the dot at the bottom-right to the bottom-left, and the red triangle to column 1 with its right angle now on the right: (a). (d) moves the triangle but does not flip it.