长途电话网中,线路按其重要性分为一级线路和二级线路。
参考答案:对
根据首字母及汉语提示,完成下列单词的拼写,使句意通顺。
小题1:Hainan is a good place to go s________.
小题2:Tom and Sam are twins,but there are some d__________between them.
小题3:F_______ is quite important to everyone .We all need friends.
小题4:You should practice more to __________(提高)your English.
小题5:I am _________(口渴的)and I world like something to drink.
金属网假顶处于什么样的情况时可能发生推垮型冒顶?