TOEFL Listening: TPO-TOEFL阅读TPO - 520NCHR74C5Q9UGRN$

What is the author's purpose in presenting the information in paragraph 7? A. To compare the influence of volcanoes and solar activity on climate variability with the influence of factors external to the global climate system B. To indicate that there are other types of influences on climate variability in addition to those previously discussed C. To explain how external influences on climate variability differ from internal influences D. To argue that the rapid warming of Earth in recent decades cannot be explained