Which of the following is correctly states as it happens in the common cockroach?

In cockroach, mandibles are a pair of hard, strong, large, dark coloured traingular, structures which move in horizontal motion and crush food between them. Gizzard or proventriculus has an outer layer of thick circular muscles and thick inner cuticle forming six highly chitinous plate called teeth. The gizzard acts as the grinding chamber and helps in grinding the food particles.