we have to ___(is) useful when we use fire

When there is a fire,we have to learn＿＿＿ to call we have to be ___ when we do everything. sometimes fire is useful,it's ()we must be ()w We use b__ to keep warm when it is cold. the internet is very useful.we can use it( )english ( )useful information we have! We don't have to ___ the electricity we don't use.A afford B It is not until ___ the things ___ we used to have ___ we le We have to ___ ___ ___ him . 英语翻译We must have water to live .If the water we use is not c learned,fire,is,when,to,we,what,do,there,a 连词成句 英语翻译We have no idea about when man first began to use salt,b