Answer:
Probably A, can't see all of D
Explanation:
I can't see the last of D, so I will still try.
A function means that each x only goes to one y, but each y can have multiple xs going to it. If that's hard to understand, on the table, if you have two of the same xs on the x side, they HAVE to have the same y on the y side. Simple as that.
Right away, A looks right since it doesn't repeat anything on the x side, it has 4, 5, 6 and 7. Let's look at the others.
B repeats 3, but the ys are different, one has 10 and one has 30, so this isn't a function. They would both have to be 10 or 30 or some other number.
C repeats -5 and both have a different y, 2 and 3, so not a function
D I can only see the first two x entries so I can't be sure, so maybe you can tell. If there is any repeat int he x side and the corresponding y side isn't the same then it also isn't the function. i have to assume there is a repeat though.