Final answer:
In Book 20 of the 'Iliad,' Zeus commands the other gods to remain neutral in the conflict, aligning with option (a).
Step-by-step explanation:
In Book 20 of the Iliad, Zeus commands the other gods to remain neutral in the conflict between the Trojans and the Greeks. This command allowed for human heroes to determine the outcome of their battles without divine interference, reflecting a shift in the narrative that focuses on the mortal contingencies of war.
Although the gods were heavily involved in other parts of the epic, Zeus's decree in this book is a notable exception, providing an opportunity for the Trojans and Greeks to fight it out among themselves, showcasing their valor and skills as warriors.
The neutrality of the gods is a consistent narrative element in various historical and mythological texts, even paralleled by human conflicts such as the initial American neutrality in the American Revolution.