The diagonal elements of the coefficient matrix obtained by applying the least-square to Cartesian grids are ___________

• A. the ratio of the grid sizes and the weights in the x, y, z-directions
• B. the product of the grid sizes and the weights in the x, y, z-directions
• C. the weights in the x, y, z-directions
• D. the grid sizes in the x, y, z-directions