The most common reason is a condition called idiopathic (unknown cause) thrombocytopenia (low platelets) purpura (ITP). Platelets are blood cells which aid is blood clotting.

最常见的原因是突发性(原因不明)低血小板紫癜(itp)，血小板是帮助血液凝结的血细胞(其实血小板不具有细胞结构——译者注)。

youdao

The real reason that businesses fail to take advantage of the full power of XQuery is fear of the unknown.

对于那些未能利用XQuery的全部威力的公司，真正的原因是害怕未知事物。

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His worried parents took him to several hospitals, but the reason for his obesity remains unknown, though it is possibly due to his dietary habit, according to local media.

他的父母很担心，带他求医无数，但是肥胖症的原因还是很难查清楚，也许是因为当地饮食习惯，他的膳食调配也影响着他的体重。

youdao

While the reason for the phenomenon is unknown, some scientists believe the electrical activity is due to the proximity of the sea-level lake to the Andes.

BBC: Venezuela��s Andean playground

The reason all money would initially go into money market accounts is a largely unknown peculiarity in the way the feds now keep Social Security records: Employers send in Social Security taxes in lump sums periodically throughout the year.

FORBES: Fact and Comment

"Part of the reason that it's valued is that it's kind of an unknown entity, " he says.

FORBES: 12. Respiratory Therapist