Is the group each user belong to stored in a SQL database or anything that Forms could pull from? If not, you would need to hardcode the rules for each individual.

This can be done using field rules and some an additional field. Add a field (single line) to the form and hide it using a CSS style like so .dontshow {display: none;} then assign the dontshow class to the field. have the default value of the field be the variable currentuser (choose from the arrow in Forms). Now in the field rules you would need to create the rules that govern which drop down fields are viewable when. If you have all the users and the group they belong to in a database, you could add a second field with the group name that gets populated based on the current user variable. Then in your field rules, you could simply look at what group the user is in and hide the correct drop down fields. If you don't have that information in a database, you will need to make rules for each person and what drop down fields need to be hidden.

I hope that helps.