Verified answer

To laugh at somebody/something = rire de. So your sentence would be, 'Les gens ont ri de son invention.' 'laugh at his' would be: the conjugated form of rire + de + sa/son/ses. Also, since 'invention' starts with a vowel, you use 'son' and not 'sa' even though the word is female. Hope that helped =P.

Les gens ont ri/se sont moqué de son invention.

Laugh at : rire de, se moquer de.

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