it is A that ～(Aこそが～である): It is the teacher that makes the class interesting. (クラスが面白いのは先生です) - 試験に出る! 英単語検索辞書

it is A that ～(Aこそが～である): It is the teacher that makes the class interesting. (クラスが面白いのは先生です)

It is the teacher that makes the class interesting.