Babies have established some kind of "model" in their minds about the external world, forming a certain view of the external world. If this model conforms to the external world, they are satisfied; if not, they are dissatisfied when the desired result does not appear. According to the meaning of this passage, if a baby smiles at a face he is familiar with, does that mean? ['he likes this person.', 'This face looks kind.', 'He expects to consolidate some kind of "model" in his mind.', 'This face fits with a certain expectation in his mind.']