这本书的前言解释了作者的写作动机。
The ___preface of this book explains the author's motivation for writing it.
他在演讲前先简短地介绍了背景知识。
He ___prefaced his lecture with a brief introduction of the background.
作者在序言中简要介绍了本书的创作背景。
The author included a short ___preface explaining the background of this book.
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