下列哪些与操作系统安全配置的原则符合（）？
A.安装最新的补丁程序
B.关闭没必要的服务
C.关闭没必要的服务
D.开放更多的服务
参考答案：A, B, C
China sent up two manned spaceships and they were also great scientific _______ in the world.
A．campaigns
B．surprises
C．achievements
D．discoveries
齿轮供油泵出口需不需加止回阀？
