Which of the Following BEST Describes an Example of Child

Which of the following BEST describes an example of child development as a system?

A) Juan's rate of learning new words accelerated tremendously between 18 months and two years of age.
B) Robyn has been crawling for several months, and soon she will be able to pull herself up to a standing position.
C) Sharyl understands conservation of quantity, but one year ago she thought that a tall, thin cup held more orange juice than a short, wide cup.
D) Naren has begun to talk, and his social interactions with his child care provider have changed.
E) Lilith is 36 inches tall and she is adding about four inches a year.