Kidneys are concerned with the functions of ...... and .........

Explanation

**Step-by-Step Solution:**

1. **Identify the Organ**: The question asks about the functions of the kidneys, which are vital organs in the human body.

2. **Understand the Primary Function**: The kidneys are primarily involved in the excretion of waste products. They filter blood to remove waste substances, which are then excreted in the form of urine.

3. **Define Excretion**: Excretion is the process of eliminating waste products from the body. In the case of the kidneys, they excrete urea and other nitrogenous wastes.

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