The correct option is D Leaflet
In a sweet pea, tendrils are modified leaflet. A tendril is a specialized stem, leaf or petiole with a threadlike shape that is used by climbing plants for support, attachment and cellular invasion by parasitic plants, generally by twining around suitable hosts. They do not have a lamina or blade, but they can photosynthesize. They can be formed from modified shoots, modified leaves or auxiliary branches.
Thus, the correct answer is option D.