CREATING MULTIPLE DROP-DOWN LIST BASED ON PRIOR CHOICE

Hello, 

I am having to create a form that will require drop down options. I learned how to create a drop-down, but how do you create a new drop-list based on the selections from the previous drop down list?

Ex: Column A has 3 options: Med, Vision, Dental. 

Column B would have the drop down list based on the selection choice from Column A

Column C would have the drop down list based on the selection choice from Column B

The header would be: 

Column A - BENEFIT  

Column B - PLAN

Column C - AMOUNT CHARGE

I appreciate your time and effort educating me on creating this. 

Regards, 

HR