Common European Framework of Reference for Languages.
Hughes, A. (2016). Testing Oral Ability. In Testing for Language Teachers, publ. by B. Chandler, http://slideplayer.com/slide/5285432/ as of Aug. 30, 2016.
Supriyato, J. (2013). Testing Oral Ability. In Beautiful World, http://jokosuper.blogspot.com/2013/01/language-assessment-testing-oral-ability.html as of 2013.