1 Routine screening of average-risk women should begin at age 50, instead of age 40. 2  Routine screening should end at age 74. 3  Women should get screening mammograms every two years instead of every year.4  Breast self-exams have little value, based on findings from several large studies. Routine screening of average-risk women should begin at age 50, instead of age 40. 2  Routine screening should end at age 74. 3  Women should get screening mammograms every two years instead of every year.
in chemical compound: Alkynes. Molecules that contain a triple bond between two carbon atoms are known as alkynes. The triple bond is made up of one Ï bond and two Ï bonds. As in alkenes, the Ï bonds constitute regions of increased electron density lying parallel to the carbon-carbon bond axis.
an alkane is a hydrocarbon containing only single bonds an alkene contains one or more carbon carbon double bonds alkynes have one or more carbon carbon triple bonds aromatic hydrocarbons contain a circular pattern of double and single bonds where the double bonded electrons can travel completely around the ring