If L and H divorced, then H could marry
I) D only
II) F
III) D or G
II or III, but not both
Clearly H can't marry any one of E, I, J, and K (direct descendants). Further, A, M, B, and C are married. So we have to consider F, G and D. Now, F and G are of different sexes. Also, since B and C are of different sexes, and B and D are also of different sexes, so C and D are of the same sex. G is of the same sex as C. So, G and D of the same sex. Thus, H can marry either (D or G) or F, whichever is male.