Pick one of the 8 possible solutions depicted below the thin horizontal line, to fill in as an answer for the bottom right blank picture. Unfortunately, I cannot remember and thus quote the source of this puzzle, but I am confident it is a good one.
I think it is:
In each row, the line style (plain, dotted, arrows) is consistent. That means the last item in the third row has to have "arrow" style. This eliminates patterns 8, 4, and if you look closely, 6 and 7 (there is one plain line in each of patterns 6 and 7).
As you work left to right on any given row, the number of line intersections increases. Row one goes
1,2,3; Row two goes
1,5,9; row three goes
1,3,?. So the qualified pattern must have more than three line intersections. That gets rid of patterns 1, 2, and 5. Pattern 2 is an oddball which "suggests" intersections just outside the frame, but there's no precedent for that in the other patterns.
Pattern 3 has correct line style for all its lines, and it contains 5 intersections. This fulfils another rule, which is that the increment of intersections is consistent in a given row:
1,2,3 => increment 1,
1,5,9 => increment 4,
1,3,5 => increment 2