31.   Police and school officials said they did not know the cause of the melee.

32.   So we feel stressed out, not knowing the cause.

33.   Sluter said the cause will be known only after investigations are complete.

34.   The cause is not known, but the first sign is usually a series of tiny red bumps that grow larger, gradually becoming red plaques with silvery scales.

35.   The cause was not known late Wednesday.

36.   The bacteria is a less common, though potentially more dangerous, cause of infections known as enterococcus, acquired in the hospital.

37.   The condition is more common in women than in men, and its cause is not known.

38.   The disease has been virtually eliminated, now that the Fore Highlanders of New Guinea know the cause and abandoned the cannibalistic rituals.

39.   The investigators have determined that the center fuel tank exploded, but they do not know the cause.

40.   The officials said they did not know the cause of the collision, which occurred during daylight.