Learn French: Le responsable a lu les réclamations et les a comprises. - The manager read the complaints and understood them.

This is the core rule of your current lesson! The word les (meaning them) is a direct object pronoun that comes before the verb. Because les replaces les réclamations (a feminine plural noun), the past participle compris must agree with it by adding -es.

Why doesn't lu also get an -es at the end? The manager read the complaints too!

In the first half of the sentence, the direct object (les réclamations) comes after the verb a lu. When a verb uses avoir in the passé composé, the past participle only changes if the direct object comes before it. Since it comes after, lu stays in its basic default form.

How do we know les réclamations is feminine?

A very handy trick in French is that almost all nouns ending in -tion are feminine. Recognizing this helps you know that any pronoun replacing it later (like les) will trigger feminine agreements, like the -es on comprises.

What is the basic form of the past participle for comprendre?