What are three current business factors that are influencing customer decisions in making technology investments?（） ["return on investment","competitiveness","number of product features","day one costs","regulation","availability of budget"]
（）是根据商品需标量和成本合理化确定采购批次、间隔和批量，以确保在不间断供给的前提下使成本最小化。 ["采购决策","库存决策","运输决策","生产决策"]
移架前应做（）准备工作。 ["操作前，清除顶.底板及其他影响支架各有关部件动作的障碍物","检查液压管路是否齐全完整，胶管不得被矸石挤卡或埋压","检查各部管接头是否连接可靠，发现U型卡松动，接头损坏或漏液等现象应立即进行处理","检查泵站向工作面支架液压系统的供液是否正常"]
安全边际指标的表现形式有（）。 ["安全边际量","安全边际额","安全边际率","保本作业率","保利量"]
用钢尺丈量两段距离：D1＝180.56 m±0.04m，D2＝254.45m±0.04m；求每段距离的相对中误差。
请简答五种混交方法。
