The correct answer is D: Liver.

The liver is the organ responsible for producing bile, which is essential for the digestion and emulsification of fats in the small intestine.

Here’s why the other options are incorrect:
- A: Gall bladder: The gall bladder stores bile produced by the liver, but it does not produce it.
- B: Pancreas: The pancreas produces digestive enzymes and bicarbonate, but not bile.
- C: Spleen: The spleen is involved in filtering blood and recycling red blood cells, but it does not produce bile.
- E: Stomach: The stomach is involved in the digestion of food but does not produce bile.

Thus, the liver is the organ that produces bile.