reference sound source

例句：

1. 1. The book is a great reference for learning English.
   这本书是学习英语的很好的参考资料。
2. 2. She quoted the passage from her textbook as evidence.
   她引用了课本中的一段话作为证据。
3. 3. He cited his research paper as proof of his theory.
   他引用了他的论文作为他理论的证据。