Bobomurodov Sirojiddin Mengziyo Ugli 2023. PRINCIPLES OF SELECTING MATERIALS FOR THE FORMATION OF FIRST INVARIANT AND VARIABLE CONCEPTS ABOUT NATURE IN PRIMARY CLASS STUDENTS. European International Journal of Multidisciplinary Research and Management Studies. 3, 01 (Jan. 2023), 84–91. DOI:https://doi.org/10.55640/eijmrms-03-01-14.