假设函数g: A → B 和f: B → C ,其中A = {a, b, c, d}, B = {1, 2, 3}, C = {2, 3, 6, 8}, g = {(a, 2),(b, 1),(c, 3),(d, 2)} 和 f = {(1, 8),(2, 3),(3, 2)}. 则 f 的逆函数为
A. {(8,1),(3,2),(2,3)}
B. 不存在
假设函数g: A → B 和f: B → C ,其中A = {a, b, c, d}, B = {1, 2, 3}, C = {2, 3, 6, 8}, g = {(a, 2),(b, 1),(c, 3),(d, 2)} 和 f = {(1, 8),(2, 3),(3, 2)}. 则f ◦ g =
A. {(a,3),(b,8),(c,2),(d,3)}
B. 不存在
C. { (b,8),(c,2)}
D. { (a,3),(b,8),(c,2)}