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.
Beisbol: El receptor, atrapar
Baloncesto: Driblar, el cesto
Tenis: La red, la pelota
Sophie y Charlie estan <em><u>trabajando</u></em> en una finca de café.
Hope it helps! :)