Final answer:
The combining form nas(o) is related to the nose and does not directly correspond to any of the provided options, as it specifically refers to the nasal area, not the cornea (d), eardrum, hearing, or the mastoid process.
Step-by-step explanation:
The combining form nas(o) is related to the nose. The closest definition to nas(o) among the provided options is the cornea which is 'd.' However, this is actually not the correct association for nas(o), which specifically pertains to the nose, not the cornea.
None of the other options (eardrum, hearing, mastoid process) are directly related to the nose either. The cornea is part of the eye and the eardrum and mastoid process are parts of the ear. For example, the term nasal refers to something related to the nose, and the paranasal sinuses are air-filled spaces around the nasal cavity.