Geographic range is the maximum distance at which a light may be seen under（）. ["existing visibility conditions，limited only by the curvature of the Earth","perfect visibility conditions，limited only by the curvature of the Earth","existing visibility conditions，limited only by the intensity of the light","perfect visibility conditions，limited only by interference from background lighting"]
SolidWorks草图绘制中“直线”与“中心线”只是线型不同，用途是相同的。
在有序的社会交往结构中，以诚相待和言必有信，既是交往中必要的条件，也是交往双方应尽的基本责任。（）
传统证券投资组合管理的投资程序包括：（）。 ["制定投资政策","证券投资分析","构建并修正证券投资组合","分别用期望收益率和收益率的方差来度量投资的预期收益水平和风险，建立均值方差模型，进而做出投资决策"]
装载机仪表盘上的气压表指示制动系统储气罐充气压力，当指示压力为（）时，不准许装载机起步。 ["0.75MPa以上","0.45MPa以下","0.45～0.55Mpa","0.55～0.75MPa"]
何谓难筛粒，易筛粒？他们在筛分过程中的行为如何？
