What do the underlined words “on the brink of” in the first paragraph most probably mean?

(单选题)______, British scientist Steven Hawking opened an account o (单选题)The book was so interesting that he had read it for four hou (单选题)Please choose a person to ______ your group to take part in (单选题)Smile costs ______, but it gives so much, so we should learn (单选题)President XI Jinping welcome online criticism from netizens, (单选题)Tom is really smart. In fact, I don’t believe anybody in his (单选题)This author writes this passage to______. (单选题)For this woman, cultural divergences_______. (单选题)Multicultural couples might encounter the followings except (单选题)The second paragraph shows that_______.