【单选题】【消耗次数：1】
CPU状态分为核心态和用户态，从用户态转换到核心态的途径是（ ）。
①
运行进程修改程序状态字
②
中断屏蔽
③
系统调用
④
进程调度程序
参考答案：
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在下列选项中，不属于造成某进程状态从等待态__________就绪态变化的原因是（）
①
有更高优先级的进程要运行
②
该进程占用的外围设备工作结束
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该进程等待的资源得到满足
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该进程等待干预的故障被排除
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_______ Tom ________ Mary can help me, for they are very busy.
①
Either；or
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④
whether；or