✔ 最佳答案
Katie Leung-- She joined the audition herself...
Emma Watson (Hermione Granger) -- she was picked by some Warner Brothers staff in her school.
Rupert Grint (Ron Weasley) -- He joined the audition himself...
Daniel Radcliffe (Harry Potter) He met the producer of the film (David Heyman) during one of his visits to the cinema with his parents and was picked.
參考: Some news articles, a book, and my self =]