Dimitrova, Lilia http://orcid.org/0000-0001-7538-2777
Georgieva, Gergana http://orcid.org/0000-0003-3515-9524
Trifonova, Petya
Oinakov, Emil
Protopopova, Valentina http://orcid.org/0000-0002-1776-0220
Metodiev, Metodi http://orcid.org/0000-0002-2950-9105
Article History
Received: 13 November 2019
Accepted: 31 January 2020
First Online: 14 February 2020
Compliance with ethical standards
:
: The authors declare that they have no conflict of interest.