Eustress is best defined as:
Go with C — Beneficial stress. Within Endocrinology, that statement lines up with the standard definition and the usual exam wording you’ll see. In plain terms, this is mainly a definition check, and Beneficial stress is the standard term or meaning used in Endocrinology. Holding that picture in mind makes Beneficial stress feel natural rather than something you only memorise. Link the term to a real body example (organ, tissue, or ion flow) so the idea stays concrete under exam pressure. A short mental diagram helps — start from stimulus or structure, follow the pathway, and stop at the functional result described by Beneficial stress.
Ref: Animal physiology is Unit 7 of the CSIR NET Life Science Syllabus, covering core body systems. It accounts for roughly 10% of the total marks in Sections B and C.