The main reason why they were so excited is that pandas are just so cute!

他们如此兴奋的主要原因是熊猫实在太可爱了！

Sadly, human activity is the main reason why the number of monarch butterflies is falling.

可悲的是，人类活动是帝王蝶数量减少的主要原因。

The reason why English is spoken everywhere is that in the nineteenth century, English became the language of world trade.

各地都说英语的原因是，在19世纪，英语成为了世界贸易用语。

This is the prima reason why we need to act now.

这是我们现在需要行动的主要的原因。

Refraction is the reason why a fish in water appears closer to the surface than it actually is.

折射是为什么水中的鱼看起来比实际更靠近水面的原因。

The reason why humans keep curious.

人类保持好奇的原因

In other words, there's a reason why people like to gamble.

换句话说，人们喜欢赌博是有原因的。

There's another reason why I wanted a chat with you before Monday.

我想在周一之前跟你聊聊还有另一个原因。

Maybe this is the reason why I dropped my cup of tea.

可能这就是我掉一杯茶的原因吧。

That's the reason why this little cross is so important to me.

这就是这个小十字架对我如此重要的原因。