WhatisnecessaryforasubjecttohavereadaccesstoanobjectinaMulti-LevelSecurityPolicy?什么对于主体在多层安全策略中拥有对一个客体的访问权限是必要的？（） A: Thesubject'ssensitivitylabelmustdominatetheobject'ssensitivitylabel.主体的敏感性标识必须支配客体的敏感性标识 B: Thesubject'ssensitivitylabelsubordinatestheobject'ssensitivitylabel.主体的敏感性标识从属于客体的敏感性标识 C: Thesubject'ssensitivitylabelissubordinatedbytheobject'ssensitivitylabel.主体的敏感性标识被客体的敏感性标识从属 D: Thesubject'ssensitivitylabelisdominatedbytheobject'ssensitivitylabel.主体的敏感性标识以客体的敏感性标识为主体