TOEFL Reading: ETS-TOEFL阅读机经 - 9646M793T1P60NMXL$

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. A. The foundational species become obvious once the system has collapsed. B. Ecosystems will not collapse as the foundational species do not exist. C. It is clear that the system would fall apart if it did not have its foundational species. D. Without the collapse, the foundational species are not obvious in the ecosystem.