Question: Variables are defined dynamically. When you log$-$in to a system, no variables are defined. In the course of running, a program will define variables via the READ $($R$)$ and SET $($S$)$ commands, and undefine variables via the KILL $($K$)$ command. Notice that commands can be abbreviated to one letter. As you know, there are two kinds of variables string and numeric. AVariables are defined dynamically. When you log$-$in to a system, no variables are defined. In the courseof running, a program will define variables via the READ $($R$)$ and SET $($S$)$ commands, and undefinevariables via the KILL $($K$)$ command. Notice that commands can be abbreviated to one letter.As you know, there are two kinds of variables string and numeric. A variable may be defined via aREAD com