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Les déchets doivent être triés avant la collecte.

Les déchets doivent être triés avant la collecte.
The waste must be sorted before the collection.
From Lesson 387:Passive voice with modal verbs (pouvoir / devoir être)·French

Questions & Answers about Les déchets doivent être triés avant la collecte.

How is the passive voice formed with the modal verb devoir in this sentence?
To form the passive voice with a modal verb, you conjugate the modal verb (doivent), add the infinitive of the verb to be (être), and then add the past participle of the main action verb (triés). This perfectly matches the English structure must + be + sorted.
Why is there an s at the end of triés?
In the passive voice, the past participle always agrees in gender and number with the subject of the sentence. Since Les déchets is masculine plural, the past participle triés takes an s.
Why is waste translated as the plural noun Les déchets?
While waste or garbage is typically a singular, uncountable noun in English, French commonly uses the plural form les déchets to refer to household or industrial waste. Because the subject is plural, the verb must also be the plural doivent.
Could I use devant instead of avant for before the collection?
No, you must use avant here because it refers to time or sequence (happening earlier in time than the collection). The word devant is used only for physical location, meaning physically in front of an object or place.

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