Final answer:
The most common life-cycle stage in bryophytes, such as mosses, should be the gametophyte.
Step-by-step explanation:
In bryophytes, such as mosses, the most common life-cycle stage should be the gametophyte. Bryophytes spend most of their life cycle as gametophytes, which are haploid and responsible for sexual reproduction. The sporophyte stage in bryophytes is relatively smaller and dependent on the gametophyte.