The answer should be the Hepatic portal vein.
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The correct answer is B. Oxygen.
Oxygen, as a part of the atmosphere, also participates in UV protection, besides being necessary for breathing.
veterinarians and zoologists work with animals in a professional capacity.
Veterinarians primarily provide medical care to animals that are kept as pets or livestock on a farm.
Zoologists are researchers who primarily focus on understanding the relationship between wild animals and other animals or their habitat.
The cells of the immune system can be categorized as lymphocytes (T-cells, B-cells and NK cells), neutrophils, and monocytes/macrophages. These are all types of white blood cells. The major proteins of the immune system are predominantly signaling proteins (often called cytokines), antibodies, and complement proteins