11.   Rosenberg and Walker had been planning to withdraw the drugs soon anyway, to see if the virus would come back a second time.

12.   Scientists believe that virus came from a nonhuman primate.

13.   That is to give the officials time to determine whether other animals have been infected and where the virus may have come from.

14.   The virus most likely came to the lions through contact with spotted hyenas who raid village dumps.

15.   The viruses come from leaking septic tanks.

16.   The virus came to a dead end.

17.   The virus may have come from the Philippines, possibly making it an Internet Asian flu.

18.   When that happens, the virus ordinarily comes roaring back, resuming its advance to full-blown AIDS.

19.   When new viruses come along, your program needs those new signatures to find them.

20.   Will the West Nile virus come to Texas?