Kelp and laver belong to algae plants, with simple structure and no differentiation of roots, stems and leaves. Common algae plants include Dianthus, Undaria pinnatifida and Chlamydomonas.

B, pteridophytes, there are roots, stems, leaves differentiation, as well as Azolla, Selaginella, Osmunda and so on. Mistake.

C, bryophytes, rootless, with stem and leaf differentiation, in addition to wall moss, cucurbit moss, etc. C error.

D seed plants include gymnosperms and angiosperms. gymnosperms have roots, leaves and seeds, and angiosperms have roots, leaves, fruits and seeds. D error.

So choose: a