Clear cell contents of drop down box based on condition

In an Excel template, I have a simple Y/N list to select for the field 'Travel Required.' If 'Yes' is selected the field 'Select Travel Level:' appears in column B and a list box in the column C reveals the type of travel for selection - light, heave, international, per diem. Here's my issue. If 'No' is selected in the Travel Required field, I have a formula in column B to blank out 'Select Travel Level' and I want to also blank out column C for travel type selection. I'm not sure how or if it can be done with a formula to clear the contents of a list box. I'd prefer not to use VBA to accomplish this if at all possible.


Travel Required: Yes
Select Travel Level: Light Travel(drop down selection if travel is selected 'Yes')


Travel Required: No
Light Travel(drop down list blank if 'No' is selected for Travel Required)

Thanks in advance for any help provided!!

P

See if attached example will help using Defined Names in Data Validation in B1 and B2

That works perfectly. Thank you SO much!!