71.   Two doctors from the Centers for Disease Control and Prevention in Atlanta came to Harvard Yard to investigate possible causes of the outbreak.

72.   Transportation officials were investigating the cause of the accident.

73.   Whatever the twisted motive, prosecutors are right to investigate the causes and recommend safeguards, though it may well be that no safeguard will work perfectly.

74.   Pacific Bell will investigate the cause of the outage as soon as service is restored, Britton said.

75.   Police and fire officials are investigating the cause of the accident, Meruk said.

76.   Police are investigating the cause of the explosion.

77.   Police are investigating the cause of the Yokohama accident.

78.   Police are still investigating the cause of the fire.

79.   Police asked the United States embassy and the Colombian Air Force to investigate the cause of the crash.

80.   Police contacted by telephone refused to talk to foreign reporters except to say they are still investigating the cause of the explosion, which left no survivors.