At present, scientists and clinicians do not understand why some patients experience a much more severe clinical course, though research is under way.

目前，科学家和临床医生不明白为何一些患者会出现极为严重的临床症状，他们正对此进行研究。

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A great quantity of sediment deposited on the lower river course and riverbed gradually raised and suspended is the essential reason of severe threatening of floods in the lower Weihe river.

大量的泥沙淤积在下游河道，河床逐渐淤高，是渭河下游水患威胁严重的根本原因。

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Heading into the open, the stock is off more than 13%, placing RIMM on course for a severe gap lower this morning.

FORBES: RIMM Runs Red on Slow BlackBerry Shipments

Usually the virus runs its course in a year or so without severe symptoms--men, in particular, rarely realize they've got it, blithely passing it on to their partners.

FORBES: Cornering A Killer

Usually the virus runs its course in a year or so without severe symptoms--men, in particular, rarely realizing that they've got it, blithely pass it on to their partners.

FORBES: Cornering A Killer