1. S + V(=be動詞) + C(=that節)
    a. The difference is that they use their whole bodies.
    b. The trouble is that he has no friends in this town.
    c. The biggest problem is that we have little time to practice the play.
  2. 前置詞 + 関係代名詞
    a. Alaska was the fiftieth state in which they had performed.
    b. The singer about whom she wrote in the magazine is coming to Japan this spring.
    a’. Alaska was the fiftieth state (witch) they had performed in.
  3. 関係副詞when
    a. Wednesday is the day when I am very busy.
    b. The day will come when such a question will never be asked again.