5. Let A, B, and C are three sets. Which is incorrect about the difference set? (A) (A-B)-C = A -(BUC)；(B)(A-B) -C = (A-C) - B；(C) (A-B) -C= A-(BnC)； (D) (A- B)-C=(A-C)-(B-C).

複選題3. Suppose we have two functions fand g, withf(1)=3,f(2)=1,f(3)=4,f(4)=6, g(1)=5,g(2)=3,g(3) =4,g(4)=1,g(5) =3,and g(6) = 2. Which is the correct mapping of the composite function g o f? (A) go f(1) = 5； (B) go f(2) = 3； (C) go f(3) = 1； (D) g o f(4) = 6.