Data Validation, clear data if parent dropdown is changed

Hi

My spreadsheet consists of drop down menu's that are reliant on the previous drop down.

Let's say
A1 - Sales/Variance
A2 - Type of sale or type or variance
A3 - Reason

However, I have noticed that if all three have been selected and then A1 was changed from Sales to Variance, the drop down for A2 and 3 would now not be applicable as the options are different. How would I clear this?

So far I am using Data Validation only.

Thanks