19．
It‘s a wonderful，warm summer day without a cloud in the sky．You're outside，and you can feel the sun‘s heat on your skin．Do you know what else you are feeling？You‘re feeling the sun‘s energy!Without it，the earth would be a cold，dark，lifeless place The sun‘s radiation（輻射） gives us light and heat energy．
The Sun‘s radiation can be harmful to us as well．We can‘t see it，but ultraviolet（紫外線） radiation comes from the sun along with heat and light．You can not see ultraviolet radiation，but it influences our health．Ultraviolet radiation is what burns our skin．
Ultraviolet radiation has three parts：ultraviolet radiation A，ultraviolet radialion B，and ultraviolet radialion C．Waves of ultraviolet radiation A and B may cause harm to our body when we get sunburned．The harm to our body can give us skin cancer（皮膚癌） and cause other health problems．
You can help to protect yourself from ultraviolet radiation by wearing sunscreen（防曬霜），sunglasses and hats．
Try to stay out of the sun when it is especially strong．You can find out ultraviolet radiation levels by watching the weather report on television．
76．What can we get from the sun‘s radiation？Light and heat energy．
77．Does the sun‘s heat burnour skin？No，it doesn't．
78．How many parts are there in ultraviolet radiation？There are three parts in ultraviolet radiation．
79．When do we have to keep out of the sun？When the sunlight is especially strong．
80．How can we find out ultraviolet radiation levels？By watching the weather report on teleνision．．
