Which of the following expressions must be added to the element stiffness matrix for beams supported on elastic supports, where l is length of beam element, and s is the stiffness per unit length of element?

• A. ( frac{sl}{420} begin{bmatrix}156&22l&54&-13l 22l&4l^2&13l&-3l^2 54&13l&156&-22l -13l&-3l^2&-22l&4l^2 end{bmatrix} )
• B.
• C. ( frac{EI}{l^2} begin{bmatrix}12&-6l&-12&6l -6l&4l^2&6l&2l^2 -12&6l&12&6l 6l&2l^2&6l&4l^2 end{bmatrix} )
• D. ( frac{EI}{l^3} begin{bmatrix}12&-6l&-12&6l -6l&4l^2&6l&2l^2 -12&6l&12&6l 6l&2l^2&6l&4l^2 end{bmatrix} )
• E. ( frac{EI}{420} begin{bmatrix}156&22l&54&-13l 22l&4l^2&13l&-3l^2 54&13l&156&-22l -13l&-3l^2&-22l&4l^2 end{bmatrix} )