Drop down selection validation

We are using a pdf as a training document to test users on a web based process.

We want to confirm that users have selected the correct option in the drop down field and if not show a validation to advise them to select to correct response.

We need a custom javascript that reads the "Workflow" field and validates that the response selected is "Level 1 Rebuttal"

Can anyone assist?

The code we have tried is

optionObject.selected

var x=document.getElementById("Level 1 Rebuttal").selected;

optionObject.selected=true/false

We have tried it as an Action on the  drop down field itself as well as the "review form" button on the pdf and neither work if the selection has been changed but is wrong. it only performs the validation if the selection has not changed.