答案：B

考查强调句型和同位语从句。It was at that school ______ he realized his dream把It was和______ 去掉后，剩下he realized his dream at that school，是一个完整的句子，所以是强调句型，由 that引导；______ he was going to be a teacher.是 dream的同位语从句，由 that 引导。所以选B。