--- has been announced,we shall have our final exams next mo

选B as has been 。。。表示“正如。。。所说”这句话的意思是说“正如通知所说,我们将于下月进行期末考试。” as has been 。。。是英语中常用的表达,类似的还有 as has been mentioned (above)“正如前面提到的”。