单选题   ______ is announced in today's papers, all the schools will open on September 1.
 
【正确答案】 C
【答案解析】关系词as和which均可引导非限制性定语从句,修饰整个主句。但是as引导的定语从句可置于句首,也可置于句中,而which引导的定语从句只能后置。本题正确答案为C。