English Translation
By whom was this machine invented?
“C’est qui” works too.
By whom was this machine invented?
“C’est qui” works too.
Are you sure? To transform from passive to active I think you would have to change more of the sentence, like “Celui qui a inventé cette machine, c’est qui ?”.
Disclaimer: I’m very far from being good at French.
C’est qui qui a inventé cette machine ? is acceptable and a common, albeit inelegant, phrasing.
I agree, “C’est qui qui…” is indeed “inelegant” .
I think a simpler option would be: “Qui a inventé cette machine?”, just like “Who invented this machine?” would work just fine in English.