What feature of an alternation of generations life cycle distinguishes this life cycle and a haploid life cycle?

The key feature that distinguishes an alternation of generations life cycle from a haploid life cycle is the presence of both a multicellular diploid stage (sporophyte) and a multicellular haploid stage (gametophyte). In alternation of generations, these two stages alternate, with the sporophyte producing spores through meiOSis and the gametophyte producing gametes through mitosis. In contrast, a haploid life cycle consists solely of a multicellular haploid stage, where the organism undergoes mitosis to produce gametes without a diploid stage.