71.   Since testosterone reduction is already an accepted treatment, researchers know a great deal about it.

72.   Since some of the bacteria were still dividing, the researchers knew that they were potentially viable.

73.   Some scientists also question how researchers will know whether the drugs are effective in individual cases.

74.   Still, because the virus was only isolated about eight years ago, researchers still know little about its long-term effects.

75.   Something researchers do know for sure is that a high-fat diet raises the risk of heart disease.

76.   Such damage has not been observed before, but it was not associated with illness, and researchers do not know whether it will ultimately affect health.

77.   That, he argues, is exactly what researchers still do not know.

78.   The compound must undergo years of testing in both animals and humans before researchers will know if it can help block HIV transmission.

79.   The culprit, researchers now know, is not stress but a corkscrew-shaped bacterium called Helicobacter pylori.

80.   The families that were studied in Belarus were healthy, and researchers do not know what the newly discovered mutations mean.