21.   It was, instead, like the virus isolated previously from the captive chimpanzee of unknown origin.

22.   Most aviation experts believe a spark of unknown origin in the center fuel tank caused the plane to explode over Long Island Sound.

23.   No other major X-Men character has an unknown origin.

24.   Of unknown origin, this event is unique in Portugal.

25.   Pepper lore is packed with mystique, fueled by sketchy research, unknown origins, questionable categorizing techniques and even confusing spelling variations of chile.

26.   Resistance to the changing paradigm is perhaps strongest among forensic anthropologists, whose work includes identifying human remains of unknown origin.

27.   Ryals has suffered from severe seizures of unknown origin since he was a year old.

28.   The cause was complications of sarcoidosis, a disease of unknown origin that results in lesions and had affected his heart, his family said.

29.   The board said a spark of unknown origin in the tank apparently ignited the vapors.

30.   The fever of unknown origin has become an even bigger problem as immune-deficiency conditions have proliferated.