The correct option is (b) A plate is a two-dimensional analog of a beam
Easy explanation: Geometrically, plate problems are similar to the plane stress problems except that plates are also subjected to transverse loads that cause bending about axes in the plane of the plate. In other words, a plate is a two-dimensional analog of a beam. Because of the smallness of the thickness dimension, it is often not necessary to model plates using three-dimensional elasticity theory. Simple two-dimensional theories that account for the kinematics of bending deformation of thin bodies subjected to transverse loads have been developed, and they are known as plate theories.