It is not that hard. Just look up a graphing calculator.
With any of these cites, just paste in ƒ(x) = 2^x, or sometimes they won't recognize that, so put y = 2^x since that is what f(x) means.
After that, they will show you the graph. With some cites though, you have to tell them what you want them to do with your equation. All you have to do is press "graph" once you enter in y = 2^x.
Either way, they will show you the graph, so the correct graph would be the third one. :)
