these days students in some schools are asked not to use mobile phones

题目

these days students in some schools are asked not to use mobile phones
这个的主语是什么?难道不是学生吗?为什么这句话是被动语态.（我还没学）.我看到被动语态句子的结构 一般动词在人称的前面 还有个by.这句话 就不是啊.求教

答案

(1) 是被动语态: students in some schools are asked ( by their headmasters=省略了) not to use mobile phones
(2) 如不是被动语态: students in some schools are [asking] their headmasters for permission to use mobile phones.