在线等!求大神分析这句下语法...there has been a need for sth

在线等!求大神分析这句下语法...there has been a need for sth there has been a need for sth 不懂为什么是there has been?真是什么时态呢,. 改为同义句在线转换her mother has been a party member for there agos同义 在线等!求大神解释!急!语法不明白%>_ 信号与系统,求大神指点.在线等分析. 请分析两句话的语法?I have been there twice.I have learned English for He has been there for six months. He has been there for six months mr.smith____here for there weeks a :has already been b :has 求大神鉴别 在线等 语法题目疑惑It has been raining for a few days ,we must do somethi 物理电学：求A读数在线等！急~球大神！！！