Of the Following, Which Is an Appropriate Example of Systematic

Of the following, which is an appropriate example of systematic change from a developmental perspective?

A) James realizes that he has to balance his checkbook, if he wants to avoid overdraft fees.
B) Natussa would rather not hold her mother's hand when she crosses the street, as she is a "big girl" even if she is only four.
C) Now that Molly is three, she is able to climb the stair with alternating feet instead of on her knees as she did when she was two.
D) Mindy likes to play her video games even though she knows she should be studying.