Perhaps even without those options, many native speakers can instantly give or () as the most natural expression which fits in that blank. is such a common adjective to describe a friendly baby who smiles instead of crying when held by a stranger. is also commonly used to describe a friendly animal. This is a rather simple vocabulary question, so you have to memorize it.
doesn't match the definition in that sentence, and it's usually not used to describe a baby whose personality is not formed yet. I feel someone who is is usually at least three years old. We don't use to describe an animal, either.