Which of the following are necessary components of a Multi-Level Security Policy?下列哪一项是多级安全策略必需的组件？（）

• A、Sensitivity Labels for subjects & objects and a "system high" evaluation.对主体和客体实施敏感性标识以及对其进行系统高的评价
• B、Security Clearances for subjects & Security Labels for objects and Mandatory Access Control.对主体和客体安全标识的安全许可以及强制访问控制
• C、Sensitivity Labels for only objects and Mandatory Access Control.只针对客体的敏感性标识和强制访问控制
• D、Sensitivity Labels for subjects & objects and Discretionary Access Control.对主体及客体的敏感性表情和自主访问控制