Which of the Following Statements About the Simplification of Speech

Which of the following statements about the simplification of speech to children (CDS) is incorrect?

A) Experiments show that CDS is not helpful to language acquisition.
B) There are mixed findings about the relation between CDS and language acquisition.
C) The speech to some children contains very few of the usual characteristics of CDS.
D) Mothers of deaf children modify their sign language to children in similar ways to CDS.