先把句子还原成陈述句吧！

Listening to and viewing content are as effective as reading the written word when covering the same material. 听内容和看内容与阅读书面文字一样有用。

Listening to content 与 viewing content 是两个并列的动名词短语，用作主语；

reading the written word 是比较分句的主语（其余部分省略了）；

when covering the same material 属于连用连词 when 的现在分词短语，相当于 when one covers the same material.