数据库管理系统由三级模式组成，其中决定DBMS功能的是(20)。数据库管理系统与操作系统、应用软件的层次关系从核心到外围依次是(21)。

(102)

(103)

(101)

(100)

Melissa and Love Letter made use of the trust that exists between friends or colleagues. Imagine receiving an(66)from a friend who asks you to open it. This is what happens with Melissa and several other similar email(67).Upon running, such worms usually proceed to send themselves out to email addresses from the victim' s address book ,previous emails, web pages(68).

(97)

(98)

(96)

(95)

X.25是CCITT关于分组交换网络的通信协议，其内容包括OSI参考模型(61)；分组在X.25网中的传输方式，不含(62)；两个X.25公用分组网之间互连时，采用的互连协议为(63)；公用分组交换网的地址(编号)根据X.121建议编制，该地址中表示国别的部分有(64)十进制数；PAD的主要功有是(65)。