1. both是两者都,全部肯定.too...to..结构是有否定的意思.
全肯+否定 = 部分否定而非全否.eg. I cann't find my book anywhere.(不是everywhere)
either ... or.两者中任何一个.
2. 这确实是定语从句 where = in which.
你下面的例句里面就是,This is the factory where (in which) i work now.
而这个This is the factory. + I visited the factory last week. visit是及物动词,不用再用介词.
上面的原题,I still remember my middle school. + I spent 6 years studying in the school.
定语从句的关系副词就是相当于介词+ which