10. where is methane produced?
a in the exhaust systems of automobiles
ob in the heating systems of homes and other buildings
c in the digestive systems of livestock and certain bacteria
d in the production systems of coal-burning power plants

During an experiment, readings for blood pressure in a persons body were found to be constant . however , when he measured by a different blood pressure cuff , the readings differed by 15 points for each reading. this difference indicates that the results are