http://ci.nii.ac.jp/naid/110000487356
http://ci.nii.ac.jp/naid/110000248720
http://ci.nii.ac.jp/naid/110004818749
http://ci.nii.ac.jp/naid/110009831480
https://www.youtube.com/watch?t=80&v=udanHWNbcP0
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problematic areas of pronunciation for Japanese ESL/EFL learners. Asian EFL Journal,
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