The usual percentages of clay and metal in cermet are: A. 50%, 50% B. 60%, 40% C. 70%, 30% D. 80%, 20%

The correct answer is: C. 70%, 30%

Cermet is a composite material made from ceramic and metal. The usual percentages of clay and metal in cermet are 70% ceramic and 30% metal. This is because ceramic is a hard and brittle material, while metal is a strong and ductile material. The combination of these two materials gives cermet its unique properties, such as high strength, toughness, and wear resistance.

Option A is incorrect because it would result in a cermet that is too brittle. Option B is incorrect because it would result in a cermet that is too weak. Option D is incorrect because it would result in a cermet that is too soft.