Oh, you got bitten by this question as well  --  me also!

The correct response is "élégance certaine". The point of the question I believe, is to highlight the change in meaning when the adjective is placed before or after the noun.

Google translater I recall brings up "incontestable" but "évident", "vrai", "sûr", and "assuré" seem to rank closer as synonyms and of course it always depends upon context.

Hope that you find this helpful.