how to differentiate -is from -es sound sing/plur?
Solution 1:
In words such as these, the pronunciation of both the last vowel and final consonant change: the singular forms end in /-ɪs/ and the plural in /-iːz/ (transcriptions in IPA: /ɪs/ as the "iss" in "kiss", /iːz/ as the "eys" in "keys").