已知列表list = ['d','r','a','g','o','n']，执行一次命令list.append('s')后，print(list)的输出结果是？（ ）

['d','r','a','g','o','n']

['s','d','r','a','g','o','n']

[  ]

['d','r','a','g','o','n','s']