题型：名词解释 如图所示，位于介质Ⅰ和Ⅱ分界面上的波源S，产生两列分别沿x轴负方向与正方向传播的机械波．若在两种介质中波的频率及传播速度分别为f1、f2和v1、v2，则( )．A．f1＝2f2，v1＝v2B．f1＝f2，v1＝0.5v2C．f1＝f2，v1＝2v2D．f1＝0.5f2，v1＝v2 查看答案
题型：名词解释 Month Average Price per Dozen April $1.26 May $1.20 June $1.08 The table above shows the average (arithmetic mean) price per dozen of the large grade A eggs sold in a certain store during three successive months．If as many dozen were sold in April as in May, and twice as many were sold in June as in April, what was the average price per dozen of the eggs sold over the three-month period 查看答案
as many dozen were sold in April as in May, and twice as many were sold in June as in April, what was the average price per dozen of the eggs sold over the three-month period