If a second copy of a legendary permanent enters the battlefield, what is the result?

When a second copy of a legendary permanent enters the battlefield, the outcome is determined by the "legend rule." According to the rules, if a player controls two or more legendary permanents with the same name, they must choose one of them to remain on the battlefield, while the others go to the graveyard. Therefore, all copies except for one are not obliterated or exiled; they are simply put into the graveyard according to the instructions of the legend rule.

The correct answer reflects this situation accurately by stating that all copies are put into the graveyard. The term "all copies" may refer to instances where you control a legendary permanent and its second copy enters. Only one remains, and the rule clarifies that this is how legendary permanents interact within the game. This ensures that a player cannot maintain multiple copies of the same legendary permanent on the battlefield, preserving the uniqueness and thematic essence of legendary cards in Magic: The Gathering.