Ans. C
When you're considering PDA, acceptance by empty stack and acceptance by the final state are equivalent.
But in the case of DPDA, acceptance by the empty stack is weaker, since the language has to satisfy the prefix property.
Prefix Property: A language L has prefix property if w∈ L implies no proper prefix of w is in L.
- When you consider the language L = {an | n >= 0 }
- It does not satisfy the prefix property, so we cannot construct a DPDA with the empty stack which accepts this language.