How can you define a global variable in Karel?

Defining a global variable in Karel is achieved by using the syntax var variableName; outside of any procedures. This placement allows the variable to be accessed throughout the entire program, not just limited to a specific procedure. When a variable is declared in this way, it is stored in the global scope, meaning it can hold values and be manipulated by any procedures defined within the program. This is essential for enabling different parts of the program to share and utilize the same data, facilitating more complex behaviors and interactions.

The other options do not correctly describe how global variables function in Karel. For instance, declaring a variable within a function restricts its scope to that function only, making it a local variable. The suggestion that global variables cannot be defined contradicts the flexibility offered by Karel's programming model, and the global variableName; syntax is not recognized in Karel, as global declarations use the var keyword instead.