The reason why the injection needs repeating every year is that the virus changes.

每年需要重新注射的原因是这病毒经常变化。

《牛津词典》

The reason why I write this letter to you is that I have a problem in respect of the writing style.

我写这封信的原因是我有一个关于写作风格的问题。

youdao

The reason why I'm late is that I missed the bus.

我迟到的原因是没赶上公共汽车。

youdao

Crowley said the fact that diplomatic note from Tehran did not address concerns about Iran's nuclear ambitions is one reason why an exploratory meeting with the Iranians is so important.

VOA: standard.2009.09.11

The reason why I have "Time-ins"... This is something that I am introducing this year for the first time.

之所以进行“练习时间。,这是今年新提出的。

哈佛公开课 - 幸福课课程节选

The main reason why I say that is actually not necessarily because of what's in the museum, but because of the museum itself.

我这样说，并不一定是因为博物馆里的东西，而主要是因为这个博物馆本身。

喜欢的艺术家 - SpeakingMax英语口语达人

And the reason why is that it implies this philosophical relationship between people and machines that gives machines a certain status.

NEWYORKER: The Visionary

The reason why is that trade once again balances.

FORBES: Keynes, White, And The Battle Of Bretton Woods

The fact is, is that the reason why we wanted a vote on the full measure is because we believe in every piece of it.

WHITEHOUSE: Press Briefing