47. Which is the following relations is a function?


A.
{(3,5), (4,3), (4,1), (5,0)}


B.
{(1,0), (2,3), (2,4), (3,6)}


C.
{(3,2), (4,3), (3,1), (3,0)}


D.
{(2,4), (-1,1), (0,1), (1,1)}