stop select box multiple allowing users to select more than one option

I know this is a daft question but I have a select box with multiple='multiple' as I want it to appear as the box with the options rather than a drop down. Is there any way to keep this look but prevent the user from selecting more than one option (like what happens on a normal drop down). Using JQuery maybe. I tried removing the multiple='multiple' and adding a height 开发者_C百科but this did not work

Have you tried:

<select size="n">

?