Which relation is not a function?

Question

1)(x-2)^2+y^2=4
2) x^2+4y+y=4
3) x+y=4
4) xy=4

So, I could eliminate some answers. My answer is either its 1 or 2. Can anyone help me?

Answer 1

2)... 4y+y...?

Answer 2

oops.. i meant:

x^2+4x+y=4

Answer 3

1)y=(+ or -)sqrt(4-(x-2)^2) not a function
2)y=4-x^2-4x function
3)y=4-x function
4)y=4/x function

Answer 4

Thank you! :D