Paulina Agova
St. Cyril and St. Methodius University of Veliko Tarnovo
Bulgaria

Paulina Agova 

St. Cyril and St. Methodius University of Veliko Tarnovo, Bulgaria.

agova@abv.bg 

Donika Valcheva
ORCID iD St. Cyril and St. Methodius University of Veliko Tarnovo
Bulgaria

Donika Valcheva

St. Cyril and St. Methodius University of Veliko Tarnovo, Bulgaria. 

d.valcheva@ts.uni-vt.bg  https://orcid.org/0000-0003-2107-0190 

Oleg Asenov
ORCID iD St. Cyril and St. Methodius University of Veliko Tarnovo
Bulgaria

Oleg Asenov

St. Cyril and St. Methodius University of Veliko Tarnovo, Bulgaria. 

o.asenov@ts.uni-vt.bg

https://orcid.org/0000-0001-8385-7680