单项选择题 放大电路处于静态的意思是：（）A. 输入的直流信号为零B. 输入的交流信号为零C. 输出的直流信号为零D. 输出的交流信号为零

单项选择题 枇杷的叶子与古代乐器琵琶十分相似，故偕音而得“枇杷”之名。（ )

判断题 波速只决定于介质的性质。正确错误

单项选择题 ______ includes messages directed at retailers, wholesalers, and distributors, as well as industrial purchasers and professional such as lawyers and physicians.A.Directional advertisingB.Institutional advertisingC.Business-to-business advertisingD.Public service advertising

单项选择题 铁路衡阳北站于7月2日承运一批发往太原北站的整车雪梨，核收运费5500元，已知衡阳北站至太原北站的运价里程为1647公里，则该批货物运到期限为？天 A、5 B、6 C、7 D、8