下列各条中，对计算机操作系统的作用完整描述的是

A．它是用户与计算机的界面

B．它对用户存储的文件进行管理，方便用户

C．它执行用户键入的各类命令

D．它管理计算机系统的全部软、硬件资源，合理组织计算机的工作流程，以达到充分发挥计算机资源的效率，为用户提供使用计算机的友好界面

Which of the following best completes the passage below "Government" does not exist as an independent entity defining policy. Instead there exists a group of democratically elected pragmatists sensitive to the electorate, who establish policies that will result in their own reelection. Therefore, if public policy is hostile to, say, environmental concerns, it is not because of governmental perversity but because elected officials believe that

A．environmentalists would be extremely difficult to satisfy with any policy, however environmentally round.

B．environmental concerns are being accommodated as well as public funds permit.

C．the public is overly anxious about environmental deterioration.

D．the majority of voters vote for certain politicians because of those politicians’ idiosyncratic positions on policy issues.

E．(E) the majority of voters do not ply wish for a different policy.