英语的系表结构he must be at home是系表结构吗,it must be terrible to be gr

英语的系表结构he must be at home是系表结构吗,it must be terrible to be gr Darling ,it must be terrible to be grown up . It must be terrible to be grown up. ‘Darling,it must be terrible to be grown up ' it must be terrible to be grown up句中to可以不要吗 it must be terri it must be terrible to be grown up!be的作用 He must be at home 的一般疑问句 He must be at home.为什么用be? You must be home at . you must be home at it must be terrible tobe grown up请帮我分析一下这句的语法结构 it must be terrible to be grown up中to be 是个什么成分啊?