Autopopulate cell based on info selected in Data Validation list

Hi everyone. Sorry for flooding the forum (I've just created another thread), but I'm facing two independent problems.

Here I'm wondering if there is a way to automatically populate a cell as soon as previous one (with data validation list) has a value selected?

I know people usually advise to use VLOOKUPS in such cases, however I don't think this applies to my question and let me show you why:

Cell A1 is Category A, Cell B1 is Category B and Cell C1 is Category C. Each of them are data validated lists and so let's say Cat.A is Country, Cat.B is Province, Cat.C is Store size. So I select in A: England, B: Devon and C: 500 (just a random number to give an example). And so after we have all these 3 values, I'd like cell D1 to automatically show: Plymouth. Cell D1 needs all 3 previous cells to have valid data selected, otherwise it stays blank.

I suppose you can't achieve that using VLOOKUP. Is there a way to do it using data validation formulas?

thanks a bunch for any tips.