Dynamic Validation List using a qualifier column in Excel 2016

I'm creating a template that will have a Validation List drop-down.

What formula can I put in the Validation filed that will list the items in Column B only if its respective column has an "x" in it?

COLUMN A
1: x
2: x
3: x
4: x
5: x
6: x
7:
8:
9:

COLUMN B
1: Lettuce
2: Carrot
3: Potato
4: Apple
5: Pear
6: Banana
7: Sofa
8: Dining Table
9: Coffee Table