Which of the following is the primary function of the gizzard?

The primary function of the gizzard is to grind ingested food into smaller particles. This is necessary for the mechanical breakdown of food in the digestive system of birds and some other animals, since these animals lack teeth to chew and grind their food. The gizzard is a muscular, thick-walled organ that contracts rhythmically to break down food particles by grinding them against each other and against small stones or grit that the animal has ingested. The ground-up food then passes on to the rest of the digestive system for further processing and absorption of nutrients.