$\begin {array} {1 1} (A)\;\text{The elements on the main diagonal of a symmetric matrix are all zero.} \\ (B)\;\text{The elements on the main diagonal of a skew-symmetric matrix are all zero.} \\ (C)\;\text{For any square matrix $ A, \large\frac{1}{2}(A+A’)$ is symmetric}\\ (D)\;\text{For any square matrix $A, \large\frac{1}{2}(A-A’)$ is skew-symmetric.} \end {array}$
