N.H. Sharypova, A.A. Bilyalova, y R.D. Shakirova, A.I. Islamova, A.R. Valeeva. 2019. «Optionality As an Indicator of Language Development». Opción 34 (diciembre), 935-48. https://produccioncientificaluz.org./index.php/opcion/article/view/30289.