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当前学科：第一节切割和焊接
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手工钨极氩弧焊操作者应随时佩戴静电防尘口罩；操作时，尽量减少高频用电时间；连续工作不得超过（）。
A . A、6h
B . B、10h
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Most people have no idea of the hard work and worry that gointothe collecting of those fascinating birds and animals that they pay to see in the zoo.One of the questions that is always asked of me is 1 I became an animal collector in the first 2.The answer is that I have always been interested in animals and zoos.According to my parents, the first word I was able to say with any 3 was not the conventional “mamma” or “daddy”,4 the word “zoo”, which I would 5 over and over again with a shrill 6 until someone, ingroupsto 7 me up, would take me to the zoo.When I 8 a little older, we lived in Greece and I had a great 9 of pets, ranging from owls to seahorses, and I spent all my spare time 10 the countryside in search of fresh specimens to 11 to my collection of pets.12 on I went for a year to the City Zoo, as a student 13 , to get experience of the large animals, such as lions, bears, bison and ostriches,14 were not easy to keep at home.When I left, I 15 had enough money of my own to be able to 16 my first trip and I have been going 17 ever since then.Though a collector's job is not an easy one and is full of 18 ,it is certainly a job which will appeal 19 all those who love animals and 20. 请在4处填上正确答案（）
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