题目内容
印制电路板焊前准备时，没必要做好装配前元器件引脚成型。
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以山石为材料作独立性或附属性的造景布置，主要表现山石的个体美或局部的组合而不具备完整的山形的处理手法称为（）。
导电金属是指专门用于传导电流的金属材料，它具有电导率高，力学强度高，不易氧化，耐腐蚀，容易加工和焊接等特性。最常用的导电金属是铜和铝。
Router R1 sits at an Enterprise branch office, using both the Internet and a leased line to another Enterprise router for its two connectivity options back into the rest of the Enterprise network. The engineer planning for this branch decided to use the leased line for all Enterprise traffic, unless it fails, in which case the Internet connection should be used to pass traffic to the Enterprise. Which of the following is most likely to be useful on the branch router?（）
什么是线路有效长？有效长的起止点有哪些？
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