Final answer:
The correct word is 'cannot.' IDLE requires that you save a Python program module before running it to ensure the interpreter executes the correct file. Thus (option b) is right answer.
Step-by-step explanation:
The correct word to complete the sentence is B. Cannot.
When using IDLE, you cannot run a Python program module without saving it first. IDLE is an integrated development environment for Python, and it requires that a program module be saved before it can be run. This is to ensure that the Python interpreter knows which file to execute and to prevent loss of code.