很难解释是什么原因让我觉得它极为可笑。

For some unaccountable reason, it struck me as extremely funny.

《柯林斯英汉双解大词典》

猪圈边这么多人，是什么原因呢？

What can be the reason for such a crowd close by the pigsty?

youdao

是什么原因导致猎鹰数量下降如此之快？

What was causing the number of falcons to drop so quickly?

youdao

The Washington Post surveyed its readership and discovered that ask people what they thought was the most significant causes of the shooting.

华盛顿邮报》在读者中进行了调查,并且发现当询问人们,他们认为,枪杀案发生的主要原因是什么。

麻省理工公开课 - 媒体、教育、市场课程节选

You feel physiologically aroused but you're not completely sure why, and you have to make up an explanation for it.

你感觉到性觉醒,但是不能确定是什么原因，你不得不给出一个解释。

耶鲁公开课 - 心理学导论课程节选

And I also wanted you to identify why, it's also important to understand why we have these trends, not just to memorize the trend itself.

而且我还需要大家判断原因是什么，这很重要，对于我们理解,为什么有这些规律，仅仅记住这些规律是不够的。

麻省理工公开课 - 化学原理课程节选