Which structure is derived from the ectoderm?

The epidermis, hair, and nail follicles are derived from the ectoderm, which is one of the three primary germ layers formed during embryonic development. The ectoderm gives rise to structures that serve as protective barriers and contribute to the body's exterior. Specifically, the epidermis is the outermost layer of skin, providing a protective layer against environmental factors. Hair and nail follicles also originate from this layer, playing important roles in protection and sensory reception.

Other structures mentioned in the other options come from different germ layers. The mucosa of the esophagus, stomach, and intestines originates from the endoderm, while bone marrow, blood, and lymphatic tissues develop from the mesoderm. Similarly, the lens and cornea of the eye are also derived from the ectoderm, but the choice highlighting the epidermis, hair, and nail follicles is the broader representation of ectodermal derivatives, which supports the answer given.