- Isabel, los vende.
The direct complement:
To replace the accompanying noun, write a direct object. They can be replaced if it is masculine it is "lo" (singular) or "los" (plural) and if it is feminine it is "la" (singular) or "las" (plural).
In this case it is "pantalones" (pants) so it is masculine and plural, that is, it is replaced by "los".
MissSpanish