Answer:
parents' talking to him frequently
Explanation:
Observation is the primary method of learning for children, since their brain is still not developed enough to initiate learning through readings or direct practices.
If parents are talking to their baby frequently, their baby will absorb huge amount of vocabolaries throughout the days and store them in their brain. This include the meaning, pronounciation, and intonation.
Compared to the babies who do not expeirence this, babies with this type of experience will learn to speak at a much faster rate, which can explan alan's impresive number of vocabulary.
