CEF Level: Elementary
1 Regular Plurals
2 Plurals of Nouns Ending in -y
3 Plurals of Nouns Ending in -sh, -ch, -s, -z, -x

CEF Level: Pre-Intermediate
1 Plurals of Nouns Ending in -o
2 Plurals of Nouns Ending in -f and -fe

CEF Level: Intermediate
1 Mutation Plurals
2 Plurals of Nouns Ending in -f and -fe

CEF Levels: Upper-Intermediate / Advanced
1 Foreign Plurals, Part 1
2 Foreign Plurals, Part 2
3 Foreign Plurals and Irregular Plurals