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入射光跟平面镜夹角为25°，入射光线与反射光线的夹角为______，要使反射光线跟入射光线成直角，入射角应为______．

答案

入射光跟平面镜夹角为25°，则入射角为90°-25°=，65°，反射角与入射角相等，则反射角等于入射角等于65°，入射光线与反射光线的夹角为

65°×2=130°；

要使反射光线跟入射光线成直角，则反射角等于入射角等于90°×

1
2
=45°．

故答案为：130°；45°．

阅读理解

阅读理解。         
        Different weather makes people feel different. It influences (影响) health, intelligence (智力) and
feelings.      
         In August, it is very hot and wet in the southern part of the United States. People there have heart trouble
and other kinds of health problems during this month. In the Northeast and the Middle West, it is very hot at
some times and very cold at other times. People in these states have more heart trouble after the weather
changes in February or March.
         The weather can also influence intelligence. For example, in a 1983 report by scientists, IQ (智商) of a
group of students was very high when a very strong wind came, but after the strong wind, their IQ was 10%
lower. The wind can help people have more intelligence. Very hot weather, on the other hand, can make it lower. Students in many schools of the United States often get worse on exams in the hot months of the year (July
and August).Weather also has a strong influence on people's feelings. Winter may be a bad time for thin people.
They usually feel cold during these months. They might feel unhappy during cold weather. But fat people may
have a hard time in hot summer. At about 18℃, people become stronger.
          Low air pressure (气压) may make people forgetful. People leave more bags on buses and in shops on
low-pressure days. People feel best at a temperature of about 18℃.
          Are you feeling sad, tired, forgetful, or unhappy today? It may be the weather's problem.

1. ________ can cause problems on health.
[ ]
A. Hot and wet weather
B. A strong wind
C. Warm weather
D. Low air pressure
2. A report shows that people may have more intelligence when ________ comes.
[ ]
A. rain
B. a strong wind
C. very hot weather
D. low air pressure
3. According to (根据) the writer, fat people may feel bad in ________ weather.
[ ]
A. cold
B. cool
C. warm
D. hot
4. The writer wants to tell us that ________.
[ ]

A. hot and cold weather influences all people in the same way
B. weather influences people's behaviour
C. IQ changes when weather changes
D. people feel good on low pressure days

5. The best title (标题) for this passage is ________.
[ ]
A. Hot Weather Causes Health Problems
B. Different Weather Makes People Feel Bad
C. Weather Influences Feelings
D. Weather Influences Health, Intelligence and Feelings
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