Final answer:
Avian red blood cells are elliptical or elongated.
Step-by-step explanation:
In mammals, including humans, red blood cells do not have a nucleus and are usually biconcave disc-shaped.
However, in some species, such as avian (birds), red blood cells have a different shape.
Avian red blood cells are elliptical or elongated.
Therefore, the correct answer is option 4) Avian.