It is not known what causes the disease.

这种病的起因不明。

《牛津词典》

As yet it is not known whether the crash was the result of an accident.

迄今尚不知该撞击是否是由于一起事故。

《柯林斯英汉双解大词典》

It is not known when the draft will become law.

该草案何时正式通过为法案目前尚不得知。

youdao

It is not known if the stories helped the company's sales, but they became extremely popular.

VOA: special.2009.01.24

Elizabeth Taylor Not Elizabeth Taylor. It is Lisa Kudrow, Lisa Kudrow known as Phoebe on "Friends."

也不是，这是“

麻省理工公开课 - 化学原理课程节选

The time was in the early 70s, so factory farming was not well-known, was not as dominated as it is today, but it still existed.

那时是70年代早期，工厂化养殖并不为很多人所知,也不如今天这样占主导地位，但当时已经出现了这种方式。

普林斯顿公开课 - 人性课程节选

The crazy food-fighting festival of La Tomatina began in 1945, but it is not known why.

BBC: Spain's La Tomatina festival

It is not known if the confirmed site was one of the original seven.

BBC: Ash tree

It is not known whether they were eaten by predators, stolen or escaped from their cages.

BBC: Komodo dragons missing from Indonesian zoo