as 是关系代词,引导定语从句,在从句中作宾语.their teachers give them books.
窍门：解这类题的关键是看后面有没有差宾语,如差,则用such as 否则用such that．
不懂再问那为什么AB不行呢给你看两个例子:This is such a difficult problem that all of us can't work it out.句中，that是从属连词，引导结果状语从句，在从句中不作成份。This is such a difficult problem as all of us can't work out as 是关系代词，引导定语从句，在从句中作宾语。（注意这个句子里面没有上一句的it这个宾语）所以AB都不行