涉及领域的宗旨和主题事项的沟通。
Field is concerned with the purpose and subject-matter of communication.
的词汇所有作家的变化时间，地点和主题事项。
The vocabulary of all writers changes with time, place, and subject-matter.
它的目的是主题事项的介绍，并提供概括了主要的概念和关系。
It is designed to introduce the subject matter and provide an overview of the key concepts and relationships.
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