While other levels involve physical satisfaction-the feeding, comfort, safety, and transportation of the human body-this level stresses mental needs for recognition, achievement, and happiness.

A．by experience over a long period of time
B．by experimenting with different colors
C．by trying out color on blind people
D．by developing the discipline of color psychology

A．how Von Steuben became the general of the American infantry
B．how the revolutionary forces came to be commanded by Washington
C．how Washington set about asking von Steuben to train his soldiers
D．how poorly organized the Americans were compared to the British army