设有关系R、S、T如下图所示，其中，关系T是(57)运算的结果。

Firewall is a(74) mechanism used by organizations to protect their LANs from the Internet.

In(75) programming, the user determines the sepuence of instions to be executed, not programmer.

C++ fully supports(73)programming.

(72) is the conscious effort to make all jobs similar, routine, and interchangeable.

(71 ) is the sending and receiving of the messages by computer. It is a fast, low-cost way of communicating worldwide.

In C language,(69) are used to create variables and are grouped at the top of a program block.

An(70) statement can perform. a calculation and store the result in a variable so that it can be used later.

(68) are those programs that help find the information you are trying to locate on the WWW．

(66) is a device that converts images to digital format．

In C language, a(67) is a series of characters enclosed in double quotes．