Is the following Python code valid?

>>> a=frozenset([5,6,7])
>>> a
>>> a.add(5)

A. Set B. List C. Tuple D. Dictionary

A. add() B. insert() C. append() D. extend()

A. remove() B. delete() C. discard() D. pop()

A. Returns the number of elements in the set or tuple B. Converts the set or tuple to lowercase C. Converts the set or tuple to uppercase D. Removes the last element