41.   Health officials are testing local water towers to try to determine the source of the infection.

42.   Health officials are testing water towers to try to determine the source of the infection.

43.   Health officials had not determined the source of the apparent pollution, but on Sunday were testing animals believed killed by it.

44.   Health officials have not determined the source of the bacteria.

45.   I believe that the only way to solve the haze problem is to determine the source and remove it.

46.   Investigation is underway to determine the source of the fire, the official said, speaking on condition of anonymity.

47.   Investigators have not determined the source of the noxious odors and do not know whether they are related to Aum Shinri Kyo.

48.   Investigators were trying to determine the source of the e-mails.

49.   It sent samples for analysis to determine the source.

50.   It challenged the way the EPA determined the source of the air pollution and how it considered the cost of pollution controls.