在设计数据库前，常常先建立概念模型，用(70)来表示实体类型及实体间的联系。

(54)

Password is a secret series of(73) that enables a user to access a file, computer, or program. On multi-user systems, each user must enter his or her password before the computer will respond to(74). The password helps ensure that(75) users do not access the computer. In addition, data files and programs may require a password.

(53)

(51)

In enterprises, the gateway is the computer that(71) the traffic from a workstation to the outside network that is serving the Web pages. In homes ,the gateway is the(72) that connects the user to the internet.

(49)

不同计算机中的(7)长度是固定不变的。设计算机的字长是4个字节，意味着(8)。

(47)

在设计数据库前，常常先建立概念模型，用(70)来表示实体类型及实体间的联系。

与十六进制数AC.E等值的十进制数是(1)，等值的入进制数是(2)。