What will be the result of the following code in Python: x = { "a": 1, "b": 2, "c": } print(x) Generates an error, because dictionary keys must have a value. Generates an error, because strings cannot be used as dictionary keys. {'a': 1, 'b': 2, 'c': } {'a': 1, 'b': 2, 'c': None}