美国国防部安全标准定义了4个安全级别，其中最高安全级提供了最全面的安全支持，它是 _______。
A．A级
B．B级
C．C级
D．D级
参考答案：A
解析：[知识点] 信息安全的基本概念
[评析] 美国国防部在1985年正式颁布了《DoD可信计算机系统评估标准》。在这个标准中，对于计算机系统的安全等级做了七级划分：D，C1，C2，刚，B2，B3，A。其中D级为最小保护，几乎没有专门的机制进行安全性保护。在以后的各级中，逐渐加强对用户访问权限的控制。
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