下面两行代码运行的结果是？（ ）
x = ['a', 'b', 'c', 'd'] print(list(enumerate(x)))
( {'a','b','c','d'} )
[(0, 'a'), (1, 'b'), (2, 'c'), (3, 'd')]
['a','b','c','d']
(['a','b','c','d'] )