Function or not?

The graph below can display 6 different relations. Choose a relation using the selectboxes. Then, drag the vertical line by the diamond to check each relation to see if it is a function. Make sure to only have one relation selected at a time. [br]1. Which relations are functions?[br]2. Can functions zig-zag up and down? Can they zig-zag left to right?[br]3. Can a function have the same y-value more than once? (Can more than one point have the same y-value in a function?)[br]4. Can a function have the same x-value more than once? (Can more than one point have the same x-value in a function?)

Information: Function or not?