text: Around this river, Henry Walter Bates's decade-long study of butterflies led to a pioneering biology paper on mimicry.
full_question: Around this river, Henry Walter Bates's decade-long study of butterflies led to a pioneering biology paper on mimicry. This river's basin contains large amounts of charcoal-rich terra preta soil. This river is home to an aquatic mammal which turns pink when excited, a dolphin called the boto. This largest habitat of the bony-tongued arapaima fish joins a darker-colored tributary at the (*) Meeting of Waters after a sandy-colored upper section often called the Solimoes. It empties into the ocean near Marajo Island and rises near Iquitos, the largest city in the world inaccessible by road. The Rio Negro, which rises in Colombia, joins this river at the rainforest city of Manaus. For 10 points, name this longest river in South America.
first_sentence: Around this river, Henry Walter Bates's decade-long study of butterflies led to a pioneering biology paper on mimicry.
raw_answer: Amazon River