The immediate cause of death is unknown.

造成死亡的直接原因不明。

《牛津词典》

If an unknown person enters a home, the camera will send the owner a warning that will cause an alarm to sound on the owner's smartphone.

如果一个不知名的人进入家中，摄像头就会向主人发送警告，并在主人的智能手机上响起警报。

youdao

Or there may be an as yet unknown cause of some cardiovascular pathology.

也可能有某种至今未知的原因导致心血管疾病。

youdao

The exact cause is unknown. But in a recent study, an experimental drug showed signs of halting the disorder in laboratory mice.

VOA: special.2010.05.19

Then on April thirtieth, two thousand seven,a huge fire of unknown cause almost completely destroyed South Hall.

VOA: special.2009.08.21

If hoarseness continues or the cause is unknown, doctors should perform an examination called a laryngoscopy.

VOA: special.2009.09.02

Such glitches have been observed in other pulsars before, but their cause is unknown.

MSN: Oddball pulsating star hiccups as it spins

The cause is unknown -presumed to be multifactorial- with signs noted in early childhood related to abnormalities in behavior, language, and social development.

FORBES: Stem Cell Therapy To Treat Autism?

The cause is unknown, but genetics appear to play a role.

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