Suppose the specification for the ADT for the Python dictionary type includes the signature:

$D.$ keys: $K$

Which of the following can we deduce from this signature alone?

That Python dictionaries have an operation called keys$()$ that returns an element of set $K.$

That Python dictionaries have a method called keys$().$

That the keys$()$ operation takes no parameters.

That the keys$()$ operation definitely has at least one precondition.

That Python dictionaries have an operation called keys$()$ that returns a list of all the keys in the dictionary.

That elements of set $D$ have an operation called keys$()$ that returns an element of set $K.$