1. The problem is to form a question in French using inversion with the elements given: "Les amis - ils mangent à la cantine ?". 2. In French, to form a question with inversion, you invert the subject pronoun and the verb. 3. The subject pronoun here is "ils" and the verb is "mangent". 4. Invert "ils" and "mangent" to get "mangent-ils". 5. Place "Les amis" at the beginning as it is the topic. 6. The correct question is: **Les amis mangent-ils à la cantine ?** This means "Do the friends eat at the canteen?" in English. Final answer: **Les amis mangent-ils à la cantine ?**