12. A complicated choreography involves a row of 7 dancers equally spaced on a flat stage; in front of the row of dancers, there is an identical, parallel row of the same number of male dancers. The choreographer wants to assign to each dancer some male dancers in such a way that, by drawing on the stage the segment connecting the position of each dancer to that of the male dancers assigned to her, there are no segments that intersect except at the ends. She also wants the total number of segments drawn to be 13. How many ways are there to make the assignments that satisfy these properties?
(A) 128
(B) 343
(C) 486
(D) 924
(E) 1716

## Numerical answer problems -5 points