Cause: unknown.

原因：未知。

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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.

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

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