Which one of the following is considered important in the development of seed habit?

Heterospory is the production of two kinds of spores, small microspores and large megaspores, as in $Selaginella$ and $Salvinia$.
The megaspores germinate into female gametophytes that are retained on the parent sporophyte for variable periods.
The development of the zygote into a young embryo takes place within the female gametophyte.
This retention and protected development is a precursor to the seed habit and is considered an important step in evolution.
A free-living gametophyte or a haplontic life cycle works against, not towards, the seed habit.
Hence heterospory is important in the development of the seed habit.