Concept:A knockout is the boxing term used when a fighter loses consciousness or cannot continue after a legal punch.
Explanation:The passage says Jim’s opponent lost consciousness after a punch to the ribs.
When a boxer loses consciousness from a legal strike, the result is called a knockout.
Option B, “knockout,” exactly matches this situation.
Option A, “luck,” refers to chance and does not describe the medical result of a punch.
Option C, “default,” means winning because the opponent fails to show up or is disqualified, which is not the case here.
Option D, “unanimity,” refers to all judges agreeing in a points decision, not to losing consciousness.
Therefore, the most suitable word for gap 80 is knockout.
Answer:B. knockout