54) Refer to Table 2.1.2. According to this production possibilities frontier, A) the opportunity cost of producing guns decreases as more guns are produced. B) a combination of 0 butter and 4 guns is attainable. C) a combination of 6 kilograms of butter and 1 gun leaves some resources unused. D) the opportunity cost of producing guns increases as more guns are produced. E) resources are equally useful in all activities