Question 87
A complicated choreography involves a row of 7 equally spaced female dancers on a flat stage; facing the row of female dancers there is an identical, parallel row of as many male dancers. The choreographer wants to assign to each female dancer some male dancers in such a way that, drawing on the stage the segment joining the position of each female dancer to those of the male dancers assigned to her, no segments intersect except at their endpoints. She also wants the total number of segments drawn to be 13. How many possible ways are there to make the assignments satisfying these properties?
(A) 128
(B) 343
(C) 486
(D) 924
(E) 1716
(A) 128
(B) 343
(C) 486
(D) 924
(E) 1716