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

So that's the main reason why we have the Heron there." Israel is one of the pioneers of combat drones, having used the remote-controlled aircraft in Lebanon and the Palestinian territories.

VOA: standard.2010.07.27

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

there is an actual reason, why for that specific job, the age is of utmost important.

能够证明就某种特定工作而言，由于特殊的原因，年龄真的至关重要。

退休很神奇 - SpeakingMax英语口语达人

The other, more recent, reason why the government needs to help U.S. exporters with financing is that other countries have greatly expanded their own financial assistance to exporters.

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The second reason why the deterrence still matters is that it deters attacks.

CENTERFORSECURITYPOLICY: Senator Kyl on nuclear deterrence

The reason why there is cost shifting is because the government has mandated that.

FORBES: Obamacare Foes Score Points, But Kennedy's A Wild Card