According to the Textbook, How Can Piaget's Ideas on Concrete

According to the textbook, how can Piaget's ideas on concrete operations be applied in the classroom?

A) by providing teachers with ideas to stimulate cognitive development
B) by helping teachers to understand that cognitive development coincides with age
C) by showing teachers that only time is needed for children to develop cognitive skills
D) by demonstrating that group discussions are a difficult teaching strategy to use in the classroom