现实生活中客观存在的群体是（） ["所属群体","实际群体","假设群体","回避群体"]
对于电子点火系来说，拨下分电器上的中央高压线对发动机机体试火时，无火花，下列说法哪个是错误的（）。 ["可能是点火线圈有故障","可能是点火控制器有故障","可能是分火头有故障","可能是信号发生器有故障"]
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【背景资料】上海A公司承接某宿舍楼工作的施工任务，在竣工后第二年发现屋面面层开裂、局部屋面及管边存在渗漏水，后经调查，施工单位在施工过程中，使用的SBS改性沥青防水卷材质量存在问题，材料进场后未进行现场见证取样，本工程屋面为3%结构找坡，设计主要做法为（由上至下）：C20细石混凝土保护层（未设计配筋），30mm厚挤塑板保温层；SBS改性沥青防水卷材；防水涂料；结构层。
请根据上述背景资料完成以下的选项。
防水层施工完成后，应进行蓄水试验，蓄水深度最浅处不能少于（），蓄水时间不少于24h。 ["10mm","20mm","30mm","50mm"]
When using the partially automated setup process, which three tasks must be completed in order to register phones with Cisco Unified CallManager Express?（） ["Configure the keepalive timer. ","Associate each phone type with a firmware file. ","Enable the firmware for each phone type being downloaded. ","Configure the dial-plan pattern to associate extensions with fully qualified e.164 numbers. ","Configure the maximum number of ephones that Cisco Unified CallManager Express will support. ","Configure an ephone for each phone being registered with the Cisco Unified CallManager Express server."]
反思文学产生的原因是什么？
