Stiffness integration for quadratic element for 2*2 matrix is ____

• A. Nt=(1-ξ)(1-η)
• B. kij=\(\sum_{IP=1}^{4}\)WIP∅IP
• C. Nt=(1-η)
• D. Nt=\(\frac{1}{4}\)(1-ξ)(1-η)