MASCULINEMost end in -i or -ovi/-evi: zakon → zakoni, grad → gradovi, kraj → krajevi. Some soften: mladić → mladići, članak → članci.
FEMININEMost -a nouns take -e: žena → žene, knjiga → knjige. Consonant-stem nouns usually take -i: stvar → stvari, noć → noći.
NEUTERNouns in -o and -e take -a: selo → sela, polje → polja, vreme → vremena.
This drill tests the nominative plural only. Serbian plurals have many irregular forms (e.g. čovek → ljudi, oko → oči, dete → deca, brat → braća, pas → psi). Learn the regular endings first, then memorise the exceptions.