The correct answer is (a) A rectangular array of binomial coefficients

Explanation: Analogous to the Lagrange family of triangular elements, the Lagrange family of rectangular elements can be developed from a rectangular array of binomial coefficients. Since a linear rectangular element has four corners (hence, four nodes), the polynomial should have the first four terms 1, x, y, and xy(which form a parallelogram in Pascal’s triangle and a rectangle in the rectangular array of binomial coefficients).