Ans.
Ruminants are those animals that gain nutrients from plant-products or foods by fermenting them in ruminant compartment before digestion. Ruminant compartment is made up of four chambers, rumen, reticulum, omasum, and abomasusm. The smallest ruminant compartment is reticulum, which helps in separation of smaller and larger food particles during digestion.
Thus, the correct answer is option D). 'reticulum.'