Authors
Asya Dragoeva
Konstantin Preslavsky University of Shumen, Faculty of Natural Sciences, Shumen, Bulgaria
Zheni Dimitrova
Konstantin Preslavsky University of Shumen, Faculty of Natural Sciences, Shumen, Bulgaria
Seliha Lyoteva
Konstantin Preslavsky University of Shumen, Faculty of Natural Sciences, Shumen, Bulgaria
Vanya Koleva
Konstantin Preslavsky University of Shumen, Faculty of Natural Sciences, Shumen, Bulgaria