His misunderstanding of language was the primary cause of his other problems.

他对语言的误解是他其他问题的主要原因。

You have to know the primary cause of it.

你必须知道的首要原因的。

A primary cause of Tom's failure is his laziness.

懒惰是汤姆失败的主要原因之一。

The primary cause of Tom's failure is his laziness.

汤姆失败的根本原因是懒惰。

But female choice probably is not the primary cause of the traits.

但是，女性的选择或许不是导致这些特征的首要原因。