In **C1** enter:

    =index(B:B,2*row()-1)

and copy downward.  In  **D1** enter:

    =index(B:B,2*row())

and copy downward:

[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/LwkUt.png

If you need to enter the formulas below row#1, replace:

    row()

with:

    rows($1:1)