12. Assume that two countries A and C can produce both timber and cars. The country A can produce 20 units of timber or 8 units of cars in one week； the country C can produce 15 units of timber or 4 units of cars in one week. If A and C trade to each other, for the country A, what is the possible terms of trade? (A) 4 (B) 3 (C) 0.4 (D) 0.33