51.   A neurologist and the medical director of the National Parkinson Foundation, the author, Lieberman, sorts through the possible causes.

52.   A neurologist and the medical director of the National Parkinson Foundation, the author, sorts through the possible causes.

53.   A. Contact lenses aside, a possible cause of a change in eye color, especially in older people, is malignant melanoma, a dangerous cancer.

54.   Administration officials did not rule out terrorism or any other possible causes.

55.   After performing an exploratory procedure on Tarpley on Friday, doctors eliminated gall stones as a possible cause of his stomach cramping and pancreatitis.

56.   Air pollution, especially ozone, was suggested but not proved as a possible cause.

57.   Although autopsy can never prove arrhythmia, he said he ruled out all other possible causes.

58.   But a member of the National Transportation Safety Board, John Hammerschmidt, declined to focus on any possible cause at a news conference at the site Sunday afternoon.

59.   But doctors have no indications about possible causes, even after extensive testing since early October and as recently as Monday, team physician Jim Muntz said.

60.   But he declined to rule out terrorism as a possible cause.