folk song的复数形式怎么拼写？

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For an encore, he sang an unaccompanied folk song.应观众再唱一曲的要求, 他清唱了一首民歌.She is humming a folk song that I never heard before.她在哼一首我以前从未听过的民歌.She was asked to sing a folk song by a large audience.许多观众要求她唱一首民歌....

folk song的音标：folk song的英式发音音标为：[fəuk sɔŋ]folk song的美式发音音标为：[fok sʊŋ]...