in order to可以看成to to vary pitch to some extent in order to maintain interest整个是真正主语,而it是形式主语
to some extent是介词短语,用作副词短语,修饰动词vary的结果.
in order to可以看成to to vary pitch to some extent in order to maintain interest整个是真正主语,而it是形式主语
to some extent是介词短语,用作副词短语,修饰动词vary的结果.