3、什么是21原则
[lbg_vp2_html5_rightside settings_id=’17’]
4、元音1-5遍
[lbg_vp2_html5_rightside settings_id=’18’]
5、元音6-10遍
[lbg_vp2_html5_rightside settings_id=’19’]
6、元音11-18遍
[lbg_vp2_html5_rightside settings_id=’20’]
7、元音19-21遍
[lbg_vp2_html5_rightside settings_id=’21’]
