问题 单项选择题

胚胎期较成年期容易建立耐受是因为( )

A.胎生期可分泌免疫抑制因子
B.有更多接触自身抗原的机会
C.有从母体获得的抑制抗体
D.免疫系统尚未发育成熟
E.免疫系统处于抑制状态

答案

参考答案:D

阅读理解

If we are driving a car or crossing a street, we will stop when the traffic lights turn red. Why do we use red rather than other colors?

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

Of all light 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 see the lights. It helps drivers slow down or stop in time. 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 light helps drivers stop in time and help prevent accidents.

小题1:______ has the longest wavelength of all light we can see.

A.Red

B.Green

C.Yellow

D.Black小题2:Red light travels farther on ______ days.

A.windy

B.sunny

C.rainy

D.cloudy小题3:Red can make people act more quickly because ____________.

A.red can make people happier

B.the scattering of red is very short

C.the scattering of red is very long

D.red can make people more excited小题4:The underlined word “prevent” means ______ in Chinese.

A.逃避

B.防止

C.处理

D.检查小题5:The passage mainly tells us ____________.

A.why accidents happen

B.how the red light travels

C.why we use red traffic lights

D.how to stop in time at traffic lights

填空题