plz help need now

Does the set of ordered pairs {(2, 100), (13, 13), (14, 5), (60, 4), (100, 1)} define a function?
A.
Yes, because each input has only one output.
B.
No, because 2 is mapped to 100 but 100 is not mapped back to 2.
C.
No, because 13 is paired with itself.
D.
No, because there does not exist a first degree equation which links the x– and y–values in the ordered pairs.