First, why on earth would Responder ostensibly sign-off knowing the 2C Opener can't possibly only hold 1 key card ?

 

Anyway, it has been suggested that holding 4 keys, you should continue by answering the trump Q-ask .

     Here, without the sQ, you would bid 6S

          But that makes no sense either.  Responder could easily have asked with 5D!

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