根据课文内容和重点短语填空

　　A．Metals are widely used in the world．It’s hard to ________　________ a world without metals．If we want to use metals well, I think it’s necessary for us to know how exactly they ________　________ different substances, for example, water．From the table we know, ________, ________ and ________ can react with cold water．And ________, ________ and ________ can react with steam．But iron only has reaction with water and steam, ________ has no reaction with them at all．

　　B．Let’s do an experiment aiming to find out if there’s a change in weight when copper burns in air．Use the following apparatus to do an experiment．Write down the method．

copper, Bunsen burner, a balance, a crucible

　　First, put the copper in the ________．Then put the ________ on the ________ and weigh it．Next heat the copper．Light the ________ and hold the ________ over it．Finally, weigh the copper again．

　　Result：It weighs a lot heavier than before．

　　Conclusion：There is a change in weight when copper burns in air．