Definite articles and singular/plural nouns

In Spanish, the definite articles el, la, los, and las must agree in gender and number with the noun they accompany. For example:

• El libro (masculine singular).

• Las flores (feminine plural).

Definite articles

a) Las ventanas están abiertas.

"Ventanas" is a feminine plural noun, so the correct definite article is las.

-Rule: The articles las and los are used with plural nouns.

b) El problema es difícil de resolver.

"Problema" is a masculine singular noun, even though it ends in -a. This is an exception to the general gender pattern.

-Rule: Some nouns, like problema or sistema, are masculine despite ending in -a.

c) Los estudiantes llegaron temprano.

"Estudiantes" is a masculine plural noun (it can refer to a mixed group or only males), so the correct article is los.

-Rule: When the gender of plural nouns is not specified, the masculine article los is used.