91.   The researchers do not know why, they said.

92.   The study was not definitive, Dr. Bristol-Power said, and researchers will know more by the middle of next year, when other studies are completed.

93.   There is no cure, and researchers do not know where the virus hides between human outbreaks.

94.   To know whether a drug will work in humans, researchers must know how the liver will respond to it.

95.   Until researchers know more, Scavia and others say they are working to find changes that benefit farmers and the gulf.

96.   What researchers do know is that the first year a child moves from elementary school to a high school campus is the most dangerous, he said.

97.   When researchers do not know what to expect in a given area, they have no way of assessing how effective their methods of trapping or sampling really are.

98.   With those illnesses, vaccine researchers knew that people who got sick and recovered also became immune and did not catch the same disease again.

99.   Women with heart disease generally fare worse than men, Goldschmidt said, and researchers do not know why.

100.   Yet despite these advances, researchers still know surprisingly little about how normal eating should be defined.