Polygon abcd is defined by the points a(-5, 1), b(-4, 3), c(-2, 7) and d(-1, 2) if the polygon rotates 90 counterclockwise to create polygon a'b'c'd', what are the coordinates of c?
a.) (-2, -7)
b.) (-7, -2)
c.) (7, 2)
d.) (2, 7)