1. The problem is to add the best topic sentence for a paragraph describing birthday celebrations around the world. 2. The paragraph mentions different birthday customs in China, Jamaica, Canada, and Vietnam, highlighting cultural diversity. 3. The best topic sentence should summarize the main idea that these customs vary globally. 4. Among the options, "People around the world celebrate birthdays in various ways." best captures the paragraph's theme. 5. Therefore, the best topic sentence is: **People around the world celebrate birthdays in various ways.**