SharePoint On Prem 2019 form rule to validate if drop down B contains (or starts with) drop down A

1. Two drop downs
2. Drop Down A - Drop Down B
3. I need a rule that will only allow people to select an option from drop down B that starts with or contains part of what was already chosen from drop down A. 

Ex:

Drop down A = “Account Balance”

Drop down B = out of the 100+ options I need to make sure people pick one of the “Account Balance - options”

Not sure on how to accomplish this so figured I’d reach out. Please let me know if the above isn’t enough information.