Option 1 -> The passage makes no mention of children's effort levels or that "they work much harder" than adults; it focuses on biological advantages instead.
Option 2 -> While children may play, the text does not cite "playing" as the reason for their success, focusing instead on their ability to learn "implicitly" by following native speakers.
Option 3 -> The text does not argue that a "need" to learn drives their success, but rather highlights that their biological makeup is the primary factor.
Option 4 -> CORRECT -> The passage explicitly credits children's "super-flexible brains" which "actually grow the connections necessary to learn an additional language" more effectively than adults.