The correct answer is D. Bone marrow.
Red blood cells are produced in the bone marrow, which is a spongy tissue found inside bones. The bone marrow is made up of stem cells, which are cells that can develop into different types of blood cells. When the body needs more red blood cells, the stem cells in the bone marrow will divide and produce more red blood cells.
The spleen is an organ that is located in the upper left abdomen. The spleen is responsible for filtering the blood and removing old red blood cells. The kidney is an organ that is located in the lower back. The kidneys are responsible for filtering the blood and removing waste products. The liver is an organ that is located in the upper right abdomen. The liver is responsible for many different functions, including producing bile, which helps to digest food, and storing glucose, which is a type of sugar.
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