You are vacuuming the floor when the vacuum cleaner suddenly stops working. You dump the contents of the vacuum, thinking it may be too full. It does not start. You remove the plug and replace it, pushing it in as far as it can go. Still nothing. You take the plug and put it into a different wall socket. It works! You have solved the problem of the malfunctioning vacuum cleaner by using

• A. insight.
• B. a heuristic.
• C. an algorithm.
• D. trial and error.