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 number of words conveyed from a mother toward her child when in conversation
C) the level of complexity of the speech a mother directs toward her child
D) the total number of words a child is exposed to as a passive listener across all listening situations