碳硫分析时发现硫元素分析时间延长且结果偏高，则需要更换（）。A、石英棉B、碱石棉C、

When the traffic lights turn red, we will stop driving a car or crossing a street. Why is red used for traffic lights instead of other colors?

As we know, scattering(散射) happens when light goes through the air. For the same media(媒质), if the wavelength islong, the scattering will be short. If the wavelength is short, then the scattering will be long.

Of all lights we can see red has the longest wavelength, so the scattering is the weakest. That means the red light travels far. In fact, it travels farther on rainy days.

Using the red light can help drivers in farther areas sec the lights. It helps drivers stow down or stop in lime. If drivers don't see the red light until they are close, they may not be able to stop the car in time. An accident may happen Red can also excite people. We can act more quickly when we see the color red. In a word, red lights help drivers stop in time and help prevent accidents.

小题1: When the traffic lights turn ______, we will stop driving a car.

A. red    B green     C. yellow

小题2:According to the passage, the scattering of the red light is the _______.

A. longest    b. weakest       C. farthest

小题3: The underlined word "wavelength" means________ in Chinese.

A.波浪        B.光波      C.波长

小题4: What can the red light help drivers do?

A. It can help drivers in farther areas see the lights.

b. It can help drivers slow down or stop in time.

C.A and b

小题5:Which of the following is the best title?

A. Why do accidents happen

b. How does the red light travel

C. Why do we use red traffic lights

下列变化中，属于物理变化的是

A．钢铁生锈

B．瓷碗破碎

C．食物腐败

D．火药爆炸

--- Have you finished the task?

--- ________ it. We still need five more days.

A．Far from

B．Rather than

C．Apart from

D．Except for

该病例最有可能诊断()

A．肺动脉内径增宽

B．动脉导管未闭

C．肺动脉瓣狭窄

D．肺动脉瓣关闭不全

E．右室流出道狭窄

能显示当前库文件中所有计算机专业学生的姓名、性别和籍贯的命令是().

A.LIST FIELDS 姓名，性别，籍贯

B.LIST FOR 专业="计算机" AND 姓名，性别，籍贯

C.DISPLAY ALL FIELDS 姓名，性别，籍贯

D.LIST FIELDS 姓名，性别，籍贯 FOR 专业="计算机\