Which of the following statements is correct for graph multiplication method?

A、The displacement of any type of structures subjected to external loads can be obtained by graph multiplication method.;

B、When EI=constant, graph multiplication method can be used for arch structures.;

C、When graph multiplication method is used, the ordinate yc in the formula is the centroid ordinate of the straight-line bending moment diagram.;

D、When graph multiplication method is used, if both bending moment diagrams are straight-line diagrams, the ordinate yc can be taken from either diagram.