Cosider the below formations of red-black tree. All the below formations are incorrect for it to be a redblack tree. Then what may be the correct order?

• A. 50-black root, 18-red left subtree, 100-red right subtree
• B. 50-red root, 18-red left subtree, 100-red right subtree
• C. 50-black root, 18-black left subtree, 100-red right subtree
• D. 50-black root, 18-red left subtree, 100-black right subtree