Read the following article and answer the question by choosing from the options.

We let them see each other for a while each day and have even put each on different sides of a glass door , and while she now appears to understand there 's another member of the family , she has n't accepted him and looks at him very angrily . He 's only been here for two days so I hope that when he grows a bit ( he 's so tiny , he does n't meow he squeals ! )

Who might be on one side of the glass door ?
Pick from:
1). A sibling
2). A kitten
3). A puppy
4). A baby...A:
2).