问题 选择题

如图所示,半圆形玻璃砖放在空气中,三条同一颜色、强度相同的光线,均由空气射入玻璃砖,到达玻璃砖的圆心位置.下列说法正确的是(  ).

A.假若三条光线中有一条在O点发生了全反射,那一定是aO光线

B.假若光线bO能发生全反射,那么光线cO一定能发生全反射

C.假若光线bO能发生全反射,那么光线aO一定能发生全反射

D.假若光线aO恰能发生全反射,则光线bO的反射光线比光线cO的反射光线的亮度大

答案

ACD

三条入射光线沿着指向圆心的方向由空气射向玻璃砖,在圆周界面,它们的入射角为零,均不会偏折.在直径界面,光线aO的入射角最大,光线cO的入射角最小,它们都是从光密介质射向光疏介质,都有发生全反射的可能.如果只有一条光线发生了全反射,那一定是aO光线,因为它的入射角最大,所以选项A对.假若光线bO能发生全反射,说明它的入射角等于或大于临界角,光线aO的入射角更大,所以,光线aO一定能发生全反射,光线cO的入射角可能大于临界角,也可能小于临界角,因此,cO不一定能发生全反射.所以选项C对、B错.假若光线aO恰能发生全反射,光线bO和cO都不能发生全反射,但bO的入射角更接近于临界角,所以,光线bO的反射光线较光线cO的反射光线强,即bO的反射光线亮度较大,所以D对,本题答案选A、C、D.

选择题
阅读理解

阅读理解。

     As China becomes increasingly urbanized (城市化), it has to find space for its urban and

rural citizens as both groups become increasingly integrated. Experts suggest a possible model

way may be "re-inventing" a "garden city".

     China's mega-cities are bursting at the borders and the country is now undergoing the quickest and

biggest urbanization in the history of mankind. It is estimated that by 2025, China will have 400 million

more people living in its cities, raising its urban population to 900 million. Besides, new satellite towns are mushrooming on the urban fringes while city ring roads are rippling outwards into the countryside at

amazing speed. Satellite maps collected by Professor Joshua Bolchover at the University of Hong Kong

bring the problem sharply into focus. They track the changing rural-urban framework in the past 30 years, and suggest that cities are cruelly destroying surrounding rural land and rapidly reducing the amount of

arable (可耕种的) land, which gives way to new residential blocks, new industrial zones, new financial

centers and the other inevitable signs and signatures of economic growth.

     This, however, is not sustainable growth pattern, especially when China has the world's largest

population to feed. So concerned urban planners are starting to note the social and physical effects of

diaspora(大移居) when replaced rural communities are forced into the cities.

     On the other hand, a trend of thought is gradually taking shape and this is the concept of the "garden

city", a combination of country and city that is being proposed by architects and city planners. Hua Li,

from Tao Architects, is among the many professionals with such a voice. His argument is supported by a

long-term study on this subject. As Hua says, the answer is to preserve patches of productive farmland

within urban boundaries. Less transportation means we have fresh agricultural products at lower costs

and less carbon emission in the city. And urban farmland can also be showcased for agricultural tourism

and education.

     The concept is already practiced at the grassroot level. Agriculture has gone into the air, up to roof

and balcony in some communities in the cities. It's common to see organic "hanging garden" on the roof

of some traditional courtyard home. According to some people, the rooftop project translate to tangible

(= practical) benefits, such as safe, nutritious vegetables, a cooler home in summer. Some say thanks to

the tomatoes they plant that are natural insect killers, there're fewer mosquitoes. Apart from these, it also

contributes to better bonding with neighbors. Zhang, a doctor in Beijing, began creating his hanging

garden five years ago. Since his garden became home to 30 kinds of vegetables and fruit -all enough to

feed his family, neighbors have enjoyed dropping by for a relaxing chat or just to see how well the lovely

vegetables and fruit are doing.

     Although people like Zhang are still rare and the greening of roof space with vegetables and fruit takes

skill and energy, with more positive media exposure and advanced technology there is the prospect that

garden city will become common practice in the near future. By then, cities will no longer look so gray

when seen from the satellites.

1. What is the purpose of paragraph 2?

A. To show the experts' concern about the increase of population.

B. To persuade people into supporting economic growth in cities.

C. To explain the reasons for the change of rural-urban framework.

D. To inform the readers of the consequences of quick urbanization.

2. In Hua Li's opinion, a combination of country and city will __________.

A. benefit the environment and lower living costs 

B. become a project that needs a long-term study

C. lead to more rural communities being replaced

D. attract more farmers to take tours in cities

3. Zhang is mentioned (Paragraph 5) to show that __________.

A. he achieves his dream to own a hanging garden

B. hanging gardens are becoming more popular

C. the garden contributes to a better neighborhood

D. he is a pioneer to practise the gardening concept

4. As for the concept of the "garden city", the writer feels_________.

A. desperate

B. hopeful

C. disappointed

D. concerned