31.   Typically, when the cause of intestinal distress cannot be pinpointed, doctors will simply continue with endscopic exams, hoping to stumble on something.

32.   Until medical officials can pinpoint the cause of the illness, the authorities are treating the case as a possible crime.

33.   While investigators have yet to pinpoint the cause of the blast, the NTSB now wants aircraft fuel tanks to be absolutely free of explosive vapors.

34.   While investigators have yet to pinpoint the cause of the blast, the NTSB is seeking to eliminate explosive fuel vapors in aircraft fuel tanks.

35.   While investigators have yet to pinpoint the cause of the blast, the NTSB now wants aircraft fuel tanks to be free of explosive vapors.

36.   While doctors could not pinpoint the cause of his cancer, Kelleher believes it is from exposure to the chemicals.

37.   While investigators have yet to pinpoint the cause of the blast, the NTSB now wants aircraft to be free of explosive fuel vapors in fuel tanks.

38.   While one evaluator noted his occasional dreaminess, the team could not pinpoint its cause.

39.   With much of the plane still to be recovered, there is hope that investigators will eventually pinpoint the cause.

40.   Pinpointing the cause of the disappearance of such aircraft is difficult because the United States often cannot reach the wreckage.