Which of the following relations is a function?
A. (1,4),(-4, 6), (1, 3), (-7, 2)
B. (1.4).(-4,2), (5, 1), (-7,2)
C. (1,0).(-4,3), (5, 1), (-4,5)
D. (5,1),(-4,4), (1, 1), (5,2)