Why does the roots, stems and leaves
constitute the vegetative past of plants?

Actually, roots, leaves, and stems are all vegetative structures. Flowers, seeds, and fruits make up reproductive structures. The roots support the plant and supply it with water and nutrients. Stems connect the roots and leaves. Plants that move water from the roots to the stems and leaves with tube-like structures are called vascular plants. ... Leaves, stems, and roots work together as a system to help the plant perform its life functions. Leaves capture sunlight and perform photosynthesis to make food for the plant.

Explanation:

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.