51.   Although CJD sometimes is hereditary, usually its cause is not known.

52.   Although the precise cause is not known, investigators are examining the possibility that the bacteria that cause the disease were spread through warm water circulating in a whirlpool.

53.   An official at the organization said he did not know the cause of death.

54.   Autopsies are routine in Greece when the cause of death is not known.

55.   Authorities did not immediately know the cause of the accident.

56.   Authorities did not immediately know the cause of the explosion.

57.   Authorities did not know the cause, but Police Chief Enio Rivera ruled out any criminal or deliberate acts.

58.   Authorities said they did not know the cause of the gas discharge.

59.   Authorities did not know the cause.

60.   Authorities in Krasnodar said they did not know the cause of the explosion or the type of gas that was emitted.