问题 填空题

白炽灯丝是由钨丝制成的,长期使用灯泡会变黑,这是因为钨丝在高温下先______,然后又______的原因.(填物态变化名称)

答案

灯泡发光时温度升高,固态钨丝升华变成气态,当灯泡熄灭时温度降低,气态钨凝华再变成固态附着在灯泡内壁,因此灯泡会变黑.

故答案为:升华;凝华.

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       Every year, wildfires(野火) destroy much forest land. homes are broken down, and thousands of

people

die. smokejumpers are stop helping to stop this.

       Smokejumpers are a special kind of firefight. they jump from places into areas that difficult to reach

by car or on foot. they race to put out fires as fast as they can.

       At a fire site, Smokejumpers first examine the land and decide how to fight the fire. their main goal is

to stop fire from spreading. using basic tools such as shovels and axes, smokejumpers clear land of

burnable material like plants and other dry material.  they carry water with them too,  but not much.

       Although most smokejumpers are men, more women are joining. Most important are your weight

and height. Smokejumpers in the U.S. for example ,must be 54 to 91 kilograms, so they don't get hurt

when they land, or get blown by strong winds.

       Smokejumpers must be able to live in the wilderness. in Russia ,many smokejumpers know how to

find food in the forest and even make simple furniture from trees.

       Theyir work is dangerous, the hours are long. But for these firefighters, smokejumpers isn't just a job.

They love being able to jump out of planes,  fight fires,  and live in the forest.  As 28-year-old Russian

smokejumpers Alexi Tishin says,"This is the best job for the strong and brave."

1. What are Smokejumpers?

                                                                                                    

2. Where do the jump from?

                                                                                                    

3. What's their main goal?

                                                                                                    

4. Why should they have proper weight?

                                                                                                    

5. What's needed to be a smokejumpers?

                                                                                                     

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