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:This school is the one you studied at 10 years ago.这所学校是你10年前上学的那个(学校).主语为this school,Is是系动词作句子的谓语,the one作表语(代指the school),you studied at 10 years ago是省略了that的定语从句,修饰前面的the one.如果school前多一个多一个the就不一样了.Is this the school__which___you studied at 10 years ago?This is the school which you studied at 10 years ago.This作主语,Is是系动词作句子的谓语,the school作表语,which you studied at 10 years ago为定语从句,修饰前面的the school.