the product is formed due to nucleophilic substitution
the product is formed according to Saytzeff's rule
conjugated double bond product is formed due to higher stability because of resonance stabilisation
(CH3)3CO⁻is better leaving group
(CH3)3CO⁻is a better base than nucleophile. Hence elimination occurs. The product formed is resonance stabilised. Hence the correct explanation is given by option C.