What is the range of the function represented by these ordered pairs?

(1, 5), (4, 5), (3, 5), (4, 6), (7, 6)

a) { 1, 3, 4, 5, 6, 7 }
b) { 5, 6 }
c) { 5, 6, 7 }
d) { 1, 3, 4, 7 }