While the exact number of these activists is unknown, Mr Loi revealed that his organisation is running at least 400 online accounts and 20 microblogs.

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The exact number of journalists who used the phone lines during that period is unknown, but more than a hundred journalists work in the offices where phone records were targeted, on a wide array of stories about government and other matters.

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But he thinks the bigger challenge is staffing a virtual hospital that might be asked to attend to the needs of an unknown number of subscribers.

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Tracking food-borne disease is also complicated by the number of illnesses thought to be caused by unknown pathogens.

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The evidence so far indicates that apo E is one of an unknown number of "housekeeping genes, " says Allen D.

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The imminent arrival of an unknown and unknowable number of Romanians and Bulgarians who are all free to work here next year is pushing it up the political agenda.

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