执行以下代码后输出的结果是？（ ）
d={1:'monkey',2:'panda',3:'bird',4:'fish'}
d[5]='sheep'
del d[3]
d[3]='dog'
print(d)
{1: 'monkey', 2: 'panda', 4: 'fish', 5: 'sheep', 3: 'cat'}
{1: 'monkey', 2: 'panda', 4: 'fish', 5: 'sheep', 3: 'dog'}
{1: 'monkey', 2: 'panda', 3: 'dog, 5: 'sheep', 4: 'duck'}
{1: 'monkey', 2: 'panda', 3: 'cat', 5: 'sheep', 4: 'duck'}