Smith's book serves as an excellent introduction to a vast subject, and will suggest plenty of further lines of inquiry.

史密斯的书是对一个广阔主题的极好介绍，并将提出许多进一步的研究方向。

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It's a useful introduction to an extremely complex subject.

这是对一门极为复杂的学科的有益入门教程。

《牛津词典》

Sets the mood. For example, if a serious subject was presented by the previous speaker, the introduction can prepare the audience for a more light-hearted speech to follow.

比如说，上一位出席发言者的主题是严肃的，那么这份介绍将让观众做好准备，去听接下来较轻松的演说。

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But even without credit, courses can serve as an introduction to a subject, supplement coursework or help with job retraining.

WSJ: College Courses Expand Online

Novelist and professor of creative writing at the university, Andrew Cowan, welcomed the introduction of creative writing at a younger stage, saying this would help students going on to study the subject at a higher level.

BBC: Creative writing to be offered at A-level