Which of the following relation is a function?
A. (11,5), (2, -8), (7, -1), (11, -6)
B. (5, 11), (-8, 2), (-1, 7), (-6, 11)
C. (-1, 11), (-8, 2), (-1, 7), (-8, -6)
D. (5, 11), (-8, 2), (-1,7), (-1, -6)