1.   The sound came from an unknown source, far away in the distance.

2.   This meant seeking out even more diverse wines from hitherto unknown sources, which further taxed the new-found art of blending.

3.   Refuse politely any cold drink from an unknown source.

4.   An aide to Dan Rather at CBS also became infected, from an unknown source.

5.   As for contracting anthrax from contaminated mail, officials advise not opening any suspicious-looking mail or any mail from an unknown source.

6.   At present, the biggest risk of human outbreaks comes from commercial development, which brings people closer to the unknown source of infection.

7.   But others said that the team had been very careful and that any unknown source of error would have to be extremely subtle to have been missed.

8.   Epidemiologists have joined the murder investigation, working round the clock to determine if the public is at risk from an as-yet unknown source of anthrax.

9.   Early on, conference participants helped one another identify hitherto unknown financing sources in their own and other communities.

10.   Experts advise discretion in opening mail from unknown sources but agree that the possibility of contracting anthrax this way is remote.