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 age 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 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 the 1900s, 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.
What does the text mainly tell us?
A.How important traffic lights are.
B.Which color has the longest wavelength.
C.What red, yellow and green can be used for.
D.Why traffic lights are red, yellow and green.
Personal computers and Internet give people new choices about how to spend their time.
We just have to keep in mind that computers and Internet offer another way of communicating. They don't take the place of any of the ways.
What's the main idea of the text?
A.Email is not an expensive way to communicate with people far away.
B.Computers and the Internet make communication more convenient.
C.Email makes it easier for people to live at home and work at the office.
D.Computers and the Internet are useful tools to keep good friendship.
Smoking cigarettes is harmful to your health. Experiments show that cigarette smoking can cause cancer. Besides the most serious and terrible cancer, cigarette smoking can also cause other health problems. For example, it can give one a "smoker's cough".
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Finally, studies have shown it is easy for cigarette smokers to catch colds. Whether you get an unimportant cold or terrible killer, cancer, smoking is harmful. Is it worth it?
What is the text mainly about?
A.Ways of experimenting on smoking.
B.Information about smoking.
C.Smoking resulting in cancer.
D.Side effects of smoking.
Alice spends her summer vacations walking back into history. Alice is 15 and she is a guide who shows visitors around the Fort(城堡) Delaware Museum in New York.
Working at the fort has helped Jane to appreciate her life even more. Alice agrees, "The fort has taught me how hard life was and how much work there was every day. We are so lucky with everything we have now. Life wasn't always this easy."
What is the main idea of the text?
A.All the jobs Alice has had at the fort have been really fun.
B.How hard life was and how much work there was in the past.
C.Reading about history can compare to experiencing it for yourself.
D.We are so lucky with everything we have now, and then we must appreciate them.
Later that day, Dad came home and said to Jessie's mom, "You didn't have to mow the lawn. I was going to do it on Saturday. It looks great. Thanks."
"I didn't mow it. Jessie did."
"Wow, our little girl is growing up!" Dad told Jessie what a great job she had done.
"It was fun, and I will do it again next week，" said Jessie.
The neighbor next door came by and asked Jessie if she wanted to mow his lawn and make some money. "Sure!" said Jessie. Jessie began mowing his lawn. Two other neighbors asked also, then another three. Jessie was now mowing lawns for them all and making some money. She was no longer bored!"I won't have time to spend my money," she laughed to herself.
What does the text mainly tell us?
A.Neighbors should learn to help each other.
B.Mowing the lawn is a good way to make money.
C.Doing something helpful can make people happy.
D.Children should help their parents at an early age.
In our daily life, robots are often found to do work that is too dangerous, boring, difficult, or dirty. And we often see kids play with toy robots.
But what exactly is a robot? There are some important characteristics(特征) that a robot must have. These characteristics might help you to decide what is and what is not a robot. It will also help you to decide what you will need to build into a machine before it can be considered as a robot. A robot has these important characteristics.
What is the main purpose of the text?
A.To help people understand what a robot is.
B.To tell what a robot can do in our life.
C.To describe the movement of a robot.
D.To introduce the history of robots.
