The most important function of the mammalian kidney is the

Options

A. control of reproduction
B. regulation of amount of protein in the blood
C. control of amount of protein in the blood
D. regulation of osmotic concentration of body fluid

Answer

**Step-by-Step Solution:**

1. **Understanding the Function of Kidneys**: The kidneys are vital excretory organs in mammals. Their primary role is to filter blood and remove waste products from the body.

2. **Exclusion of Functions**: The question asks for the most important function. We need to eliminate options that do not pertain to the kidneys' primary roles. For example, kidneys do not play a role in reproduction, ruling out any options related to reproductive functions.

3. **Analyzing Protein Regulation**: The second and third options mention protein regulation. However, proteins are too large to pass through the glomeruli of the kidneys, meaning that kidneys do not regulate or control protein levels in the blood. This eliminates these options as well.

4. **Identifying Osmoregulation**: The last option refers to the regulation of osmotic concentration of body fluids, also known as osmoregulation. This is a key function of the kidneys, as they maintain the balance of water and solutes (like salts and sugars) in the body.

5. **Conclusion**: Based on the analysis, the most important function of the mammalian kidney is indeed the regulation of osmotic concentration of body fluids. Therefore, the correct answer is option number 4.

**Final Answer**: The most important function of the mammalian kidney is the regulation of osmotic concentration of body fluids (option 4).

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