问题 填空题

一束太阳光与水平面成30°角,现要使其水平射出,那么平面镜与水平面的夹角为______或______.(按从大到小的顺序填写)

答案

因反射角等于入射角,入射光线与反射光线的夹角为入射角与反射角之和,

此时一束太阳光与水平面成30°角,则入射角为60°,

现要使其水平射出,有两种情况:当入射光线与反射光线的夹角为90°+60°=150°时,则入射角为75°,那么平面镜与水平面的夹角为90°-75°=15°

当入射光线与反射光线的夹角为90°-60°=30°时,入射角为15°,那么平面镜与水平面的夹角为90°-15°=75°

那么平面镜与水平面的夹角为75°或15°.

故答案为:75°或15°.

阅读理解

Plants are very important living things. Life could not go on if there were no plants. This is because plants can make food from air, water and sunlight. Animals and man cannot make food from air, water and sunlight. Animals get their food by eating plants and other animals. Therefore animals and man need plants in order to live. This is why we find that there are so many plants around us.

If you look carefully at the plants around you, you will find that there are two kinds of plants: flowering plants and non-flowering(不开花的) plants.

Flowering plants can make seeds(种子). The seeds are protected by the fruits. Some fruits have one seed, some have two, three or four, and some have many seeds. But a few fruits have no seeds at all. An example of a fruit without seeds is the banana fruit.

Most non-flowering plants do not grow from seeds. They grow from spores(孢子). Spores are very, very small. Some spores are so small and light that they can float in the air. We may say that spores are quite the same as seeds. When these spores fall on wet and shady(阴凉的) places, they usually grow into new plants.

小题1:What fact does the passage lead you to believe?

A.Of all living things, animals are most important.

B.Spores are seeds.

C.All fruits of flowering plants have seeds.

D.Without plants, man will die out.小题2:The paragraph following the passage will be about ________.

A.how plants can make food from air

B.how spores grow into new plants

C.why some plants have no seeds

D.why non-flowering plants are more important than flowering plants小题3:This passage is most likely to be taken from ________.

A.a story book

B.a novel

C.a science magazine

D.a laboratory report

单项选择题 B1型题