The idea that red means stop and green means go has influenced our lives in more ways than just traffic signals（信号）.We have been taught from a young ages that the color red means danger and green means it's okay to move forward.But why were those colors chosen for traffic lights in the first place？For something we have to look at every day，why couldn't they have been prettier colors？
   Well，it's important to know that before traffic lights for cars，there were traffic signals for trains.At first，railway companies used red to mean stop，white to mean go，and green to mean warn.As you could imagine，trains ran into a few problems with a white meaning go.For example，one train mistook a bright star for a white light and something unexpected happened.Because of that，railway companies finally moved green meaning go and used yellow to mean warn.And it's been that way ever since.
   Red has always been a color that meant danger，long before cars were even around.This most likely started because it's the color with the longest wavelength（波长） so it can be seen somewhere farther than other colors.
   But，believe it or not，yellow was once used to mean stop.Back in the1900s，some stop signs were yellow because it was too hard to see a red sign in a poorly lit area.Finally，highly reflective materials（高反射材料） were developed and red stop signs were born.Since yellow can be seen well at all times of the day，school zones，some traffic signs，and school buses continue to be painted yellow.
   So next time you're impatiently waiting at a traffic light，don't get so mad at them；they've certainly come a long way.

（1）What is commonly known from our childhood？

B

B

A．The color green means warn.
B．The color red means danger.
C．The color green means danger.
D．The color red means warn.
（2）Which of the following colors meant go at first？

B

B

A．Red.
B．White.
C．Yellow.
D．Green.
（3）The writer wants to show the

C

C

in the second paragraph.
A．importance of train lights
B．mistake in traffic lights
C．development of traffic lights
D．meaning of traffic lights
（4）Which of the following is TRUE according to the passage？

D

D

A．The color red means danger because it is used in traffic lights to mean stop.
B．The color with shortest wavelength is seen somewhere farther than others.
C．Yellow is used to paint school buses because of its longest wavelength.
D．Before highly reflective materials were made，yellow was used to mean stop.
（5）What does the text mainly tell us？

D

D

A．How important traffic lights are.
B．Which color has the longest wavelength.
C．What red，yellow，green can be used for.
D．Why traffic lights are red，green and yellow.