Which of the Following Lines Corrects the Error in the Map

Which of the following lines corrects the error in the Map class function?

A) Value_Type operator[ ](const Key_Type& key)
B) Value_Type& operator( ) (const Key_Type& key)
C) std::pair<iterator, bool> ret =
the_set.insert(Entry_Type(key, Value_Type() ) ) ;
D) std::pair<iterator, bool> ret =
the_set.insert(Entry_Type(key, () ) ) ;