Digital SAT : banque Reading, Writing et Math

For two centuries lichens were classified as a partnership between exactly two organisms, a fungus and an alga. In 2016 a team sequencing lichen tissue found a second fungus present in specimens from six continents, including species whose appearance had never been explained by the two-partner model. The finding did not overturn the partnership account so much as complicate it: the alga still supplies sugars, the primary fungus still supplies structure, but the third partner appears to shape the form the lichen takes. Which choice best states the main idea of the text?

For two centuries lichens were classified as a partnership between exactly two organisms, a fungus and an alga. In 2016 a team sequencing lichen tissue found a second fungus present in specimens from six continents, including species whose appearance had never been explained by the two-partner model. The finding did not overturn the partnership account so much as complicate it: the alga still supplies sugars, the primary fungus still supplies structure, but the third partner appears to shape the form the lichen takes. Which choice most logically completes the text? Before 2016, the appearance of certain lichen species _____