71.   The valve was to be checked on Friday to pinpoint the cause of the trouble.

72.   School lunches are suspected as the source of infection, but authorities have so far failed to pinpoint the cause of the outbreak.

73.   School lunches were blamed for the epidemic but authorities have failed to pinpoint the cause.

74.   The ATO team left for Japan on Tuesday to help pinpoint the cause of the explosion, an ATO spokesmen said.