The following Python code is invalid.

class demo(dict):
  def __test__(self,key):
    return []
a = demo()
a['test'] = 7
print(a)

Which of the following data types in Python is used to store key-value pairs?

A. Dictionary

B. List

C. Tuple

D. Set

What method is used to check if a key exists in a dictionary, and if not, add it with a default value?

A. setdefault()

B. addkey()

C. insert()

D. newkey()

What does the len() function do when applied to a dictionary?

A. Returns the number of key-value pairs in the dictionary

B. Returns the sum of all values

C. Returns the length of the longest key

D. Returns the length of the longest value

In Python, how can you get a list of all key-value pairs in a dictionary?

A. items()

B. get_items()

C. all_items()

D. list_items()