Final answer:
Option b) "The in-game billboards with real brands add authenticity to the game world" demonstrates effective product placement.
Step-by-step explanation:
Effective product placement in games is when the placement enhances the game experience without being distracting or disruptive to the player. In the given examples, option b) "The in-game billboards with real brands add authenticity to the game world" demonstrates effective product placement. This statement acknowledges that the product placement contributes to the immersion and realism of the game, which is a positive outcome for the advertiser.