The correlation between the sign of internal force of the beam and the coordinate system is that .
A.
the signs of shear force and bending moment are related to the coordinate system
B.
the signs of shear and bending moment are independent of the coordinate system
C.
the sign of shear force is related to the coordinate system, but that of bending moment is independent of the coordinate system
D.
the sign of shear force is independent of the coordinate system, but the sign of bending moment is related to the coordinate system