Why are the leaves of Vallisneria thin and long?

The correct options are
C To minimise the damage by strong water currents.
D To maximise the absorption of sunlight.
Leaves in submerged hydrophytes like Vallisneria are generally thin, narrow and long. These leaves offer little resistance against the water currents. Thus, plants are subjected to less mechanical stress and leaves are not easily damaged by water. Long leaves provide large surface area which allow more absorption of sunlight for photosynthesis. Thin leaves also facilitate easy diffusion of gases.