The correct option is B Diplo-haplobiontic
The term alternation of generations is used to describe a process in the life cycle of some eukaryotes. It describes an alternation in forms which occurs in plants and some protists. One form is diploid, with 2n chromosomes: the sporophyte. The other form is haploid with only one set of chromosomes: the gametophyte.
So, the correct option is "C" (Diplo-haplobiontic).