以下代码输出结果是？（ ）
ls =["2021","123","Python"] ls.append([2021,"2021"]) ls.append(2021) print(ls)
['2021', '123', 'Python', 2021]
['2020', '123', 'Python', [2021, '2021']]
['2021', '123', 'Python', [2021, '2021'], 2021]
['2020', '123', 'Python', [2021],2021]