题目内容：
根据以下材料，回答题Blind people can”see”things by using other parts of their bodies. This fact may help us to understand
our feelings about color. If blind people can sense color differences, then perhaps we, too, are affected by col-or unconsciously.
Manufacturers have discovered by trial that sugar sells badly in green wrappings, blue foods are consid-ered unpleasant, and that cosmetics should never be packaged in brown. These discoveries have grown into a branch of color psychology.
Color psychology now finds application in everything from fashion to decoration. Some of our preferenc-es are clearly psychological.Dark blue is the color of the night sky and therefore associated with calm,while yellow is a day color with associations of energy and incentive. For a primitive man, activity during the day
meant hunting and attacking, while he soon saw red as the color of blood and anger and the heat that came with effort. And green is associated with passive defense and self-protection.
Experiments have shown that colors, partly because of their psychological associations, also have a di-rect psychological effect.People exposed to bright red show an increase in breath, in heartbeat and in blood pressure；red is exciting. Similar exposure to pure blue has exactly the opposite effect ；it is a calming color.
Because of its exciting meaning, red is chosen as the signal for danger, but closer analys is shows that a vivid yellow can produce a more basic state of alarm. Sofire engines and ambulances in some advanced communi-ties are now rushing around in bright yellow colors that stop the traffic dead.
( ) How did manufactures find out that color affects states? 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.
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