柴油机的性能指标和工作参数随运转工况而变化的函数关系，称为（）。
参考答案：柴油机的特性
试结合史实，概要说明清朝前期是如何加强维护国家统一、民族团结的？
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It was announced that only when the fire was under control ________to return to their homes.
A．the residents would be permitted
B．had the residents been permitted
C．would the residents be permitted
D．the residents had been permitted
