What is the intuition behind a downward-sloping relative factor demand curve for firms?

Group of answer choices

1.Firms do not substitute inputs in response to changes in the relative price of inputs.

2.As the relative wage of an input goes down, firms substitute away from that input.

3.As the relative wage of an input goes up, firms substitute towards that input.

4.As the relative wage of an input goes up, firms substitute away from that input.