The word "it" in line 3 refers to According to paragraph 2, evidence from fossils suggests that

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问题 The word "it" in line 3 refers to
According to paragraph 2, evidence from fossils suggests that

选项 A、extinction of species has occurred from time to time throughout Earth’s history.
B、Extinctions on Earth have generally been massive
C、there has been only one mass extinction in Earth’s history.
D、dinosaurs became extinct much earlier than scientists originally believed.