____is known,John studies in____is considered the best schoo

答案：D As,what
__As__is know,John studies in__what_is considered the best school in the city.
翻译：就像大家知道的那样(众所周知),john在被誉为全市最好的学校里学习.
分析；
as is know,是as 引导的状语从句,as翻译成像……一样.这种加逗号的独立结构也不能够使用as以外的引导词充当状语.仅此一项即可选出答案.
in__what_is considered the best school in the city是介宾短语作状语,一起做study的状语,表明study的地点.what_is considered the best school in the city是what引导的宾语从句,做介词in的宾语,是一个地名.空里指代the best school,名词,表事物,所以只能用what不能用who,how,when,as等.
转载给你了,我就不去额外解释了.