Lesson 23 Bird flight鸟的飞行方法First listen and then answer the following question.听录音，然后回答以下问题。What are the two main types
新概念英语第四册第23课:Bird flight。。。Lesson 23 Bird flight鸟的飞行方法First listen and then answer the following question.听录音，然后回答以下问题。What are the two main types
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