Which one of the following best illustrates a quantitative (rather than qualitative) change in development?
A. As a 15-year-old, LaRue has started to grow facial hair.
B. Beth used to be shy around her peers, but now she's very outgoing and makes friends easily.
C. Five-year-old Mercedes has finally learned how to carry a tune.
D. Robert knows many more addition facts than he did a few months ago.
