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最佳答案:We have no matter what I do,to protect their own safety is the most important,ma
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最佳答案:(1)设改造一所A类学校的校舍需资金x万元,改造一所B类学校的校舍所需资金y万元,则x+3y=4803x+y=400,解得x=90y=130.答:改造一所A类学
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最佳答案:Safety engineering studies various accidents during human productions and activi