Which one of the following statements is true about Schmid factor: [4; 1 each] a) In polycrystalline materials, the Schmid factor varies with grain orientation but is a constant with only one value for all slip systems in each grain. b) The smallest Schmid factor is equal to 0.5, which occurs when the angle between the loading axis and the normal vector to the slip plane is 45o. c) Because Schmid factor varies with grain orientation, some grains may start to plastically deform at lower applied stress than others. d) The Schmid factor relates resolved stress normal to the slip plane for plastic deformation