three blocks,each with same mass, stacked one upon the other. the bottom block rest on a frictionlesshorizontal surface and is being pulled by a force F that is parrallel to this surface.the surface where the blocks touch each other have identical coefficients of static friction. which one of the following correctly describe the magnitude of the net force of static frection that acts on each block?
(c)fs,A=0 and fs,B=0.5fs,C
(d)fs,C=0 and fs,A =0,5fs,B