Aside from the fact that you keep repeating the code
document.getElementById("attop38") instead of assigning it once to a local variable, how is that different that the code I showed?
Oh...wait...I see...You set the <option>'s selected property to true whereas I changed the selectedIndex. So long as the <select> is not set to muliple, though, those are equivalent.
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.