Which level of Orange Book protection is considered mandatory protection and is the first level in which labels are required? A. B3 B. C2 C. B1 D. A1 Solution C. The Orange Book rates systems as one of four categories. Category A is verified protection, B is mandatory protection, C is discretionary protection, and D is minimal protection. B1 is the first level in which labels are required. Therefore, answers A, B, and D are incorrect.