Red blood cells carry oxygen in the body. In adults, they are formed in …….. .

Options

A. Liver
B. Kidneys
C. In the heart
D. In bone marrow

Explanation

**Step-by-Step Solution:**

1. **Understanding Red Blood Cells (RBCs)**: Red blood cells are responsible for carrying oxygen throughout the body. They contain a protein called hemoglobin, which binds to oxygen.

2. **Formation of RBCs in Different Life Stages**: In a developing fetus, red blood cells are primarily formed in the liver. However, as the fetus matures and grows into an adult, the site of red blood cell production changes.

3. **Identifying the Site of RBC Formation in Adults**: In adults, the primary site for the formation of red blood cells is the bone marrow. Bone marrow is a soft tissue found in the hollow centers of bones, and it is responsible for producing various blood cells, including red blood cells.

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