as debt-laden students head for degrees they think will maximize their earning potential, many vital courses suffer.

請問這句話degrees做先行詞的定語從句，that為何省略，做賓語了嗎？

As debt-laden students head for degrees they think will maximize their earning potential, many vital courses suffer.

they think will maximize their earning potential 這是嵌入式定語從句。定語從句本身是個主從復(fù)合句，they think是主句，that will maximize their earning potential為賓語從句，關(guān)系代詞that并不在主句中作成分，而是在賓語從句中作主語。關(guān)系詞所在的分句，嵌入到they think這個分句中作賓語，這種定語從句就叫做嵌入式定語從句 embedded relative clause。關(guān)系代詞在定語從句中作主語一般是不能省略的。但假如關(guān)系代詞在嵌入式定語從句中作賓語從句的主語，則是可以省略的，而且是非常容易見到的。

再給你一個嵌入式定語從句省略作主語的關(guān)系代詞的例子：

This is the book my teacher says is very useful. book后省略了that。

網(wǎng)友可以在答疑網(wǎng)搜索嵌入式定語從句“。