Which of the following was not developed by Bethesda?

The answer is Fallout: New Vegas because it was not developed by Bethesda Game Studios, but rather by Obsidian Entertainment. While Bethesda published the game, it was primarily developed by Obsidian. Bethesda Game Studios is known for developing other popular franchises such as The Elder Scrolls series and the mainline Fallout games like Fallout 3 and Fallout 4.