It is thought that the action doer is the topic focus of a passive sentence, which emphasizes the role of subject in contrast with the sentence background.

文章认为，施事在被动句中有跟句外的背景进行对比，以强调施动者是此而非彼的作用，因而是被动句中的话题焦点。

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The author also gives his own views about so-called "topic-focus" or "minor topic", and suggests considering the "topic focus" as "contrast-topic" and the "topic-reminder" as "common topic" in or…

本文认为起对比作用的话题焦点应视作“对比话题”，起一般提示作用的话题可称作“一般（或自然）话题”，从而避免使话题与焦点在概念上产生混淆。

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Students have the freedom to focus on whatever topic or subject that they are interested in and study it in depth through the internet.

学生可以自由地专注于他们感兴趣的任何主题或学科，并通过互联网深入研究。

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You start by seeding it with the name of a topic, several article links that you know are on topic, and links to profiles of people that you know focus on that topic.

FORBES: Is This What Tom Cruise Reads on Twitter?

Possibly so, but regardless of it becoming a hot topic in technology, the perception needs to shift to the focus on a hot topic in business management and organizational operations.

FORBES: Shining The Limelight On Social Business Services

As the convoluted title of this book suggests, Robert Peston struggles to focus on one topic.

ECONOMIST: The financial crisis