The second option because one same input cannot have two different outputs For example, x + 2 = y If I put in 3, y has to equal 5, nothing else. This makes the second option the only option that is a function Hope this helps!
In a function an input has a distinct output, so if I put 3 into a function and got 8, that is my answer and nothing else, if I put 3 again and get -2 then it isn't a function because I got a different answer. In the 1st, 3rd and 4th one there are two outputs for the same input so they aren't functions.
