Which of the following is true about social contexts of language development across cultures?

a. Children in developed countries speak earlier than children in traditional cultures because their parents make an effort to speak directly to them.
b. Children in traditional cultures speak earlier than children in developed countries because their mothers do not work outside the home and are able to talk with them during the day.
c. Children in traditional cultures and developed countries speak at about the same time because language is almost entirely innate in humans.
d. Children in traditional cultures hear more language around them during the day, and thus are not any slower in language development than children in developed countries where parents often use ID speech.

Answer: D