As（正如） has been announced,we shall have our exams next week.(插入语结构)
==It has been announced that we shall have our exams next week.（主语从句）
===That we shall have our exams next week has been announced (by the school).（主语从句）
===we shall have our exams next week,which has been announced (by the school).（定语从句）
=== What has been announced (by the school) is that we shall have our exams next week.（表语从句）