Final answer:
The author wants the reader to conclude that more countries will eventually adopt youth voting based on the fact that voting rights continue to change everywhere.
Step-by-step explanation:
The underlined fact in the passage states that 'voting rights everywhere continue to change.' From this fact, we can conclude that more countries will eventually adopt youth voting. This is because the passage mentions that the suffrage laws in a country can change due to internal and external forces, and voting laws contribute to the political culture of a country. As seen in examples like Austria and Brazil, countries are willing to lower the voting age, indicating a trend towards youth voting becoming more common worldwide.