Final answer:
The correct translation is "Ces papillons-là sont les plus beaux de tous."
Step-by-step explanation:
The correct translation of the sentence "Those butterflies are the prettiest of all" into French is: Ces papillons-là sont les plus beaux de tous. The word "là" is used to indicate proximity and refers to something that is further away from the speaker. In this case, it emphasizes that the butterflies being referred to are not close to the speaker.
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