Option C is correct option.

Cycas is classified as a vascular non-flowering plant because it has a well-developed vascular system (xylem and phloem) that facilitates the transport of water and nutrients, and it reproduces via seeds, but does not produce flowers.

In contrast, Marchantia (a liverwort) and Spirogyra (a green alga) are non-vascular plants; they lack a true vascular system, which limits their ability to transport water and nutrients efficiently. Dryopteris, a type of fern, is vascular but is also a non-flowering plant as it reproduces via spores instead of seeds.