Liver flukes are often found in the duct.

Bile duct.

Explanation:

The liver fluke is a parasitic worm which resides in the bile ducts and the liver of infected animals. It causes disease in humans, cattle and sheep. Clonorchis is a liver fluke parasite that get into the humans by drinking water, eating fish, crabs, eating vegetables from places where liver fluke lives. It is not contagious, can spread from infected person to healthy person. But it can live in a person for 20 to 30 years, if not treated.  

answer; (b) clear with a slight blue tint;

a population evolve