Which Statement Concerning Piaget's Theory Is True

Multiple Choice

Which statement concerning Piaget's theory is true?

A) Piaget's theory has been the source of ideas for teachers and stimulated a great deal of research.
B) Piaget's theory was never useful for teachers but did stimulate a great deal of research.
C) Piaget's theory has been the source of ideas for teachers but never stimulated research.
D) Piaget's theory was never useful for teachers and never stimulated research.