The coordinates of a quadrilateral are (5, 8), (7, 10), (9, 12), and (11, 14). After a transformation, the sign of the x-coordinate for each ordered pair has changed. Which type of transformation occurred?
A) (x,y)→(x + 2, y + 2)
B) dilation; (x + 2), (y + 2)
C) reflection across the y-axis
D) reflection across the x-axis