Which is equivalent to (4xy-3x)^2, and what type of special product is it?

It's not the difference of squares, rather it is the square of a difference. That leaves a perfect square trinomial, which narrows your selection to two choices. An expression with 2 terms is not a trinomial, so that further narrows your selection. The appropriate choice is

... (4xy -3z)² = 16x²y² -24xyz +9z², a perfect square trinomial

The expression you have in your problem statement has no z term, so none of the choices is applicable to that one.