- The main role of bile secreted by the liver during digestion is to emulsify fats to aid their digestion.
- Bile contains bile salts which have both hydrophilic and hydrophobic sides, allowing them to break large fat globules into smaller droplets.
- This process is called emulsification, and it significantly increases the surface area available for pancreatic lipase to act on fats, enhancing the efficiency of fat digestion.

- While bile does not directly activate pancreatic enzymes (Option 1), it creates an optimal environment for fat digestion.
- It also does not neutralize gastric acid in the duodenum (Option 3); this role is primarily carried out by bicarbonate secreted by the pancreas.
- Additionally, bile itself does not absorb fat-soluble vitamins (Option 4), but by emulsifying fats, it indirectly facilitates their absorption in the intestine.

Therefore, the correct answer is Option 2: Emulsify fats to aid their digestion.

Reference: Ganong’s Review of Medical Physiology, 26th Edition, Chapter 41: Digestion and Absorption