赖世雄教你学英语语法
代词
1-4：it用以强调介词短语或副词从句
其结构如下：
it is (was)+介词短语/副词从句+that从句
例：it was in 1974 that i began to study english.（我是在1974年开始学英语的。）
it was because he was lazy that he failed.（他是因为懒惰而失败的。）