Quoc: However, in some other groups, either the sporophyte or the gametophyte is very much reduced and is incapable of free living. For example, in all bryophytes the gametophyte generation is dominant and the sporophyte is dependent on it. By contrast, in all modern vascular land plants the gametophytes are strongly reduced, although the fossil evidence indicates that they were derived from isomorphic ancestors. In seed plants, the female gametophyte develops totally within the sporophyte which protects and nurtures it and the embryo sporophyte that it produces. The pollen grains, which are the male gametophytes, are reduced to only a few cells (just three cells in many cases). Here the notion of two generations is less obvious; as Bateman & Dimichele say "(s) porophyte and gametophyte effectively function as a single organism". The alternative term' alternation of phases' may then be more appropriate.

In terms of alternation of generations the pollen grains?
HW Chung: OK, some thoughts:
To answer the question, consider the following: The pollen grains, which are the male gametophytes, are reduced to only a few cells (just three cells in many cases). The answer is are reduced to only a few cells ( just three cells in many cases ).