I'm guessing, based on the answer choices, that the question is which of the answer choices is the graph of a function.
A function is a set of pairs of numbers (x, y) in which NO TWO PAIRS HAVE THE SAME FIRST NUMBER. That is, no x is paired with more than one y. Graphically, that means no points on the graph are stacked one above the other. The only answer choice that does this is the first one.
Am I right?
Next time, include the question along with the answer choices!