计算机主机和外部设备构成电子商务系统的硬件环境。（）

单项选择题The____________ became the predominant form on the chart during the explosion of Rock N' Roll in the 1950's and it's stayed there ever since. Many popular songs, particularly from early in the 20th century, are in this form, and it is often used in love songs, pop, country and rock music.

单项选择题在E-R图向关系模型转换的过程中,无论是一个1:1的联系,一个1:n的联系,还是一个m:n的联系,都可以转换为一个（ ）