Final answer:
The correct answer is A. The cornea is part of the fibrous tunic, the outer layer of the eye, which allows light to enter and is distinct from the sclera.
Step-by-step explanation:
The cornea is part of the fibrous tunic, which is the outer layer of the eye. This layer is primarily composed of the white sclera and the clear cornea, where the cornea covers the anterior tip of the eye to allow light to enter. The fibrous tunic, including the cornea and sclera, differs from other parts of the eye, such as the vascular tunic and the neural tunic or retina.
The sclera is composed of collagen and elastic fibers, while the cornea combines these elements with connective tissue and epithelia, differentiating the two components within the fibrous tunic.