1) CH2-CH-CH2-CH2

        I       I                  I

      OH    CH3          OH

2)           CH3 CH3

                 I         I 

    CH3-  C  ---- C-CH2-CH3

                I           I

              OH       OH

3)                    CH3

                         I

    CH2-CH2 -C-CH2-CH-CH3

      I                  I              I

    OH            OH           OH