单项选择题
A.increases as GNP increasesB.is reduced by credit cardsC.decreases as the average selling price of a unit of output increasesD.both A and B
A.主要频率成分B.幅值的大小C.相位D.位移E.速度
A.线性范围小B.灵敏度高C.频率范围宽D.抗干扰能力强E.不受油污等介质影响