The book also has a full answer key to all exercises.

这本书也有一个完整的答案主要向所有演习。

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This is the key to singing - learning about the art, doing practical exercises, and by listening to others who have a well-trained voice.

这是学习唱歌的唯一途径。 培养艺术感，做实际练习，听那些训练有素的歌手演唱。

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E. is a key phase to the formation of the habit of physical exercises.

学校体育阶段，则是体育锻炼习惯形成的关键期。

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