Final answer:
The completion of the sentence demonstrates an understanding that 'intractable' refers to George being stubborn and unmanageable, indicating that others knew they had to act before he made a final decision.
Step-by-step explanation:
The word 'intractable' suggests a person who is stubborn or impossible to control or manage. In the context of the sentence given, 'Because we knew that once George made up his mind, he would be completely intractable, we...' could be completed to indicate that there was an awareness of George's unyielding nature, leading to a particular course of action or attitude. A possible completion could be, 'Because we knew that once George made up his mind, he would be completely intractable, we decided to present all the facts and reasoning before he reached his final decision.'