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金属在化学反应中什么时候会变价?如何变价? 化学：变价金属有哪些?详细! 中频感应加热的原理是什么? 中频感应加热的问题现需要用中频感应加热技术加热厚度约1mm的薄铜片,加热温度需要400度,请问用直径1.5mm的纯铜作感应电极线圈,20kw以下功率的电源能不能实现.1.5mm的纯铜线圈会不会造成线 My e_mail____to you last night a sends b sentMy e_mail____to you last night a sends b sent c is sent d was sent选什么. 我要表达：请问您在2009年7月31号收到我的邮件了吗?用下面哪种说法好?为什么?Have you received my e-mail of Jul.31,2009?Did you receive my e-mail of Jul.31,2009? 一袋氧气大概要吸多长时间 “硫与变价金属生成化合物是,金属元素被氧化为底价态”中的“金属元素被氧化为底价态”怎么理解?求详解,越详细越好. 一罐氧气可以吸多久 求初二英语作文My future is to be a diplomat “未来的生活”英语怎么说,Our life in the future.这样写行吗? Not having received an answer ,she decided to write another letter .请问 having 为何 不能省略? I haven't received the letter.It()to a wrong address.A.may send B.may be sent C.might have sent D.might have been sent Instead of writhing a letter to the manager ,she decided to talk to him in person这句话怎么翻译?》 Mary couldn't have received your letter;otherwise she___ to your birthday party.A.will comeB.would comeC.would have comeD.had come答案是C、why? I haven't decided to____ ____ _____ ____ ____ ____ (是走还是留) 根正苗红 什么意思如题 一般氧气袋可以用多久? 使用氧气袋要注意什么 使用多长时间适合 42升氧气袋连续使用能用多长时间 自家的氧气袋去医院冲次氧要多少钱?42L的袋子一袋的氧气能用多久? 常见不变价金属元素都有哪些 氧气袋要要去哪里买,大概多少钱一个一个能用多长时间,用完还可以冲氧气继续用吗? 常见的活泼金属元素包括镁锌铜吗? 常见金属元素都是什么颜色?它们的氧化物又是什么颜色? My Hobby and My Future作文? 英语翻译it is friday aftenoon .we are cleaning the classroom.mike and jack are sweeping the floor .three girls are cleaning the desks and chairs .my chinese teacher is mopping the floor .l'm cleaning the biackboard .jam andbiackboard .jam and ann if you'd like to donate some money ,please call us _____55314892 这段话说的对吗 如果你想捐赠一些钱,请与我们电话联系.If you want to donate some money,please___________________.联系用call 填空：Mr Green has been___Britain for a week,and I haven't received his e-mail.I really miss himMiss Wang has moved out of the house since she a man with a lot of money.A.married with B.marriedC.married to D.got marriedMiss Li her husband two mont I have received your e-mail,I will reply to you as soon as possible什么意思麻烦翻译下