The two mandibles in the mouth part of cockroach bear teeth which cut
and masticate the food into fine particles. Gizzard is a part of
alimentary canal which is used for grinding the food as it bears six
muscles folds covered by chitinous conical plates, the teeth. Malpighian
tubules arise from the junction of mid-gut and hind-gut. Oxygen is
transported by tracheae as no pigment is present in the blood.
Nitrogenous excretory product is uric acid. So, the correct answer is 'The food is grinded by mandibles and gizzard'.