The average of four numbers A, B, C and D is 40. The average of four numbers A, B, E and F is also 40. (A, B are common). Which of the following must be true ?

A

(A + B) $$\neq$$ (C + D)

B

(C + D) = (E + F)

C

Either C = E or F; and F or E

D

C = E and D = F

E

None of these