Learn French: Il y a un problème avec ces chaussures ; l'employé les a remplacées. - There is a problem with these shoes; the employee replaced them.

Usually, verbs that use avoir in the passé composé do not change their past participle. However, here the direct object les (meaning "them") comes before the verb. Since les refers to ces chaussures, which is feminine and plural, we must add -es to the past participle remplacé to make it match.

How do we know what the pronoun les refers to?

The pronoun les means "them" and points back to the noun mentioned just before it: ces chaussures (these shoes). It acts as the direct object receiving the action of being replaced.

Why use ces chaussures instead of des chaussures?

The word ces is a demonstrative adjective meaning "these" or "those". It points to a specific pair of shoes having a problem. If the sentence used des, it would just mean "some shoes" in general.

Would the spelling of employé change if the employee were a woman?

Yes! In this sentence, l'employé refers to a male employee. If it were a female employee, you would add an extra e to make it l'employée. Both versions are pronounced exactly the same way.