Answer and explanation:
Lila's language progression comes as the direct result of her parents' encouragement. If they did not encourage her, the language development would be slowed.
In this case we are told that Lila has not been making progress for a while; however, we are told that Lila's parents keep encouraging her and consequently, her speech grows quickly. Because of her parent's reinforcement, we can conclude that Lila's speech developped thanks to all the support.
