【单选题】把债券未来的投资收益折算成现值,使之成为购买价格或初始投资额的贴现率是债券的( )。
【单选题】下列说法错误的是 ( ) A .若 a = 0 ,则 | a | = 0 B .零向量是没有方向的 C .零向量与任一向量平行 D .零向量的方向是任意的
【单选题】红宝石红色、祖母绿绿色均由Cr致色,它们属于( )
【单选题】Which of the following is NOT the principle of the Kwanzaa celebration?
【单选题】It's our duty to keep our environment____. [ ]
【单选题】Waste paper shouldn't everywhere .It's our duty to keep our city clean. [ ]