Which of the Following Is the Newest Reason to Study

Which of the following is the newest reason to study infants, among the reasons cited in the text?

A) The ability to communicate through language emerges during the first three years.
B) By three to four months of age, initially immobile infants roll over.
C) Infants who are born preterm are more likely than ever before to survive.
D) Pediatricians are interested in studying the conditions under which infants thrive.