Which type of transformation must have occurred in order to map triangle RST to its image, triangle R’S’T’?

On a coordinate plane, triangle S T R has points (negative 3, 3), (negative 1, 3), (negative 2, 1). Triangle S prime T prime R prime has points (3, 3), (1, 3), (2, 1).
a reflection over the y-axis
a translation to the right
a translation to the left
a clockwise rotation