My lovely boy, with no obvious warning, had taken his life. He left photos instead of a note.

我可爱的儿子，没有任何明显的预兆，就结束了他的生命，他留下了照片来代替遗言。

youdao

An obvious word of warning needs to be made here: quantity is not the same as quality.

这里需要做出一个明白无误地警告：科学研究的数量不能与质量相等同。

youdao

They reserve the right to tweak this algorithm whenever they feel it is necessary, often without warning or any obvious outside influence.

他们依然保留有调整这个算法的权利，只要他们觉得有必要，他们就会调整这个算法，通常都没有事先的警告，也不受外界的影响。

youdao

It's easy to work backwards through the data and see all the obvious warning signs.

CNN: Why FBI and CIA didn't connect the dots

If the risk is obvious, there's no need for a warning label--hence, steak knives don't have them.

FORBES: Magazine Article

Writing at Gameranx, Ian Miles Cheong points to a number of the other obvious flaws in the hoax letter, but sounds off with some words of warning.

FORBES: What The 'Halo 4' PR Hoax Letter Says About Gamers And Video Game Journalists