Answer:
A. and D.
Explanation:
In order to be a function every x can only have one y that is partnered with it. A. has no repeated x's so every x goes with only one y--this is a function.
B. and C. each have an x that is repeated (which is allowed, but only if the x has the same partner every time) On B. there is a -1 and it is paired with -2, but later in the list, -1 is paired with -5. This is not a function.
Same thing happens on C., there is a 4, paired with, at first a 3, then later a 0. Not a function.
D. is a function bc there is no repeated x, therefore no x's end up with more than one partner.