Which word is acceptable in an APA-style paper?

Piaget studied cognitive development mainly by

a. conducting longitudinal research studies. b. borrowing concepts from psychoanalysis. c. observing children as they solved problems. d. observing the interactions between children and their caregivers. e. observing the behavior of his siblings.

Esther Thelen and colleagues propose that coordinated, voluntary movement emerges from neurological development, parental encouragement, opportunities to exercise, and maturation of the cognitive systems

The synthesis of these interactive processes is called the A) motor development theory. B) altered states theory. C) dynamic systems theory. D) active systems theory.