问题
单项选择题
工件和焊丝上的油、锈、水等易引起焊缝产生（）。
A.咬边
B.未熔合
C.气孔
D.焊瘤
答案
参考答案：C
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工件和焊丝上的油、锈、水等易引起焊缝产生（）。
A.咬边
B.未熔合
C.气孔
D.焊瘤
参考答案：C
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| I can't remember when I started collecting litter. But it was when I got tired of 1 litter nearby that I realized no one else was going to pick it up. I live near a forest in Ohio, America. I can walk there 2 three minutes. I used to love going there to play with my dog. But one day there was 3 much litter there that I became very unhappy. I decided to clean up the forest, and I wanted to 4 happy when I went again. I made my first trip to clean the forest that afternoon. I took a big black rubbish bag with me. Ten minutes 5 I started to pick up litter, my bag was full! There were cans, bottles, broken glass and newspapers in it. From then on, I 6 to the forest four times a year to pick up litter. I often stay there for three hours. It makes me feel 7 to do something for the environment. After each trip, I look through all the litter that I've collected. If 8 of it is recyclable (可回收利用的), I'll keep it. I can't understand why people drop litter. But I will keep on picking it up 9 they stop dropping it. I know I am only doing a small bit 10 the earth, but I still think it is important. | ||||
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