相关系数的取值范围在（）相关系数越接近于1，两种证券的（）越强，证券组合的（）也越大。
简述密码体制的原则：
There are many reasons why customers lack sufficient security measures on the network. Which two reasons for insufficient security are typical of the customers today?（） ["the use of hosted email services eliminating the need for local security","the perceived costs of security solutions","the lack of risk analysis","the lack of threats to their network","the belief that free security tools are sufficient","the desire to avoid unnecessary technologie"]
Excel 97中第八列第9行单元格使用标号表示为（）。
简述软骨鱼纲的主要特征。
工频交流耐压试验的负载通常为（），试验电流在试验变压器的漏抗引起（），使试品上的电压比按变比换算的电压偏高。
