_______ runs the source code line-by-line and checks for errors.interpretervariablemoduloboolean

The correct answer is interpreter.

An interpreter executes source code directly, running it line-by-line and checking for errors as the program runs. This contrasts with a compiler, which translates the entire source code into machine code before execution, allowing for optimizations but requiring the entire program to be free of errors before execution.

Interpreters are commonly used in scripting languages like Python and JavaScript, making it easier to test and debug code since they provide immediate feedback on errors in the current line being executed. Other options like "variable," "module," and "boolean" do not directly refer to execution and error-checking processes.