题目内容：

In the traffic lights,red means "stop",green means "go",and yellow means "hurry": Why those colors, though? Why not blue,purple,and brown?The following are transponded from others WeChat.

●Red is an inherited symbol from railroads

Red symbolizes danger in many cultures,which makes sense,considering it has the longest wavelength of any color,meaning you can see it from a greater distance than other colors.Red has meant "stop" since long before cars existed,with railway signals use of red dating bake to the days when mechanical arms lifted and lowered to indicate whether the rail ahead was clear.So that one's simple.

●Green meant "caution" at first

Green's role in lights has actually changed dramatically over time.Its wavelength is next to (and shorter than) yellow's,meaning it's still easier to see than any color other than red and yellow.Back in the early days of railway lights,green originally meant "caution",while the "all-clear" light was,well,clear or white.Trains,of,course,take an unlimitedly long time to stop,and legend has it that several disastrous collisions happened after an engineer mistook stars in the night horizon for an all-clear.Thus,green became "go",and for a long time,railways used only green and red to signal trains.

●Yellow means "caution" because it's almost as easy to see as red

From the earliest days of motoring up until the mid-1900s,not all stop signs were red-many were yellow, because at night it was all but impossible to see a red stop sign in a poorly lit area.The yellow stop-sign craze began in Detroit in 1915,a city that five years later installed its first electric traffic signal,which happened to include the very first amber traffic light,at the corner of Michigan and Woodward Aves.

1.What are the earliest traffic signals designed for from the passage?

A. Cars.    B. Trains.

C. Motorcars.    D. Not mentioned.

2.Which statement is true according to the passage?

A. Green means "go" all the time.

B. Red is the easiest color to be noticed.

C. All yellow things need dealing with carefully.

D. All the three colors were once used as "caution".

3.What's the main idea of the passage?

A. What is your favorite color?

B. Why are "Red,Yellow,Green" used as traffic signals?

C. How can we figure out the wavelength of colors?

D. What color can green,yellow and red make?

4.Where is the passage from?

A. A diary.    B. A scientific magazine.

C. A newspaper.    D. The Internet.