If AC=15 and CD=4, what is BC?

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.

These graph is cross the yaxis and x axis two ways.

4, -4 is the other point it would pass through