选B,这是一个一般疑问句,把句子还原为陈述句就能看明白了:Thisschoolistheoneyoustudiedat10yearsago.这所学校是你10年前上学的那个(学校).主语为thisschool,Is是系动词作句子的谓语,theone作表语(代指theschool),youstudiedat10yearsago是省略了that的定语从句,修饰前面的theone.如果school前多一个多一个the就不一样了.Isthistheschool__which___youstudiedat10yearsago?Thisistheschoolwhichyoustudiedat10yearsago.This作主语,Is是系动词作句子的谓语,theschool作表语,whichyoustudiedat10yearsago为定语从句,修饰前面的theschool.