Using the integers -9 to 9 at the most one time each.

Ibelieve its 0 but i am not sure

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.

Distance=slopeslope is -2/4which equals-1/2the distance between these two points is -1/2