The correct option is D Volvox
In Volvox, the haploid gametophytic stage is dominant and multicellular. Hence, they exhibit a haplontic life cycle.
Fucus shows diplontic life cycle, where the diploid phase is predominant than the haploid phase in the life cycle.
Ectocarpus and Polysiphonia show haplo-diplontic life cycle where both the haploid and the diploid phases are equally prevalent in their life cyles.