Which of the Following Has Been Found to Be Most

Which of the following has been found to be most predictive of language proficiency in early childhood?

A) the extent to which a mother and child converse about objects and events to which they were jointly attending
B) the total amount of speech that a mother directs toward her child
C) the complexity of the speech a mother directs toward her child
D) the total amount of language a child is exposed to as a passive listener