The word “that” in par.4 refers to an important point the function caretaker speech

Câu hỏi :

Read the following passage  and mark the letter (A, B, C or D) on your answer sheet to indicate the correct answer to each for  the questions. Children learn to construct language from those around them. Until about the age of three, children tend to learn to develop their language by modeling the speech of their parents, but from that time on, peers have a growing influence as models for language development in children. It is easy to observe that, when adults and older children interact with younger children, they tend to modify their language to improve children communication with younger children, and this modified language is called caretaker speech.