Hello!
To change singular nouns to plural nouns, you add an -s if the ending letter is a vowel. If the last letter is a consonant, you add -es.
To change plural nouns to singular nouns, you remove the -s or -es.
To change "las casas", a plural noun, into a singular noun, it would be "la casa".
Therefore, the singular form of "las casas" is la casa.
En la manifestación del sábado pasado, los estudiantes DICEN no a la guerra
If you write in english language maybe i can help you
