$[5$ points$]$ Why is forwarding needed while adding pipelining as a functionality to a CPU?

$[5$ points$]$ Consider the following partial schematic of a MIPS CPU with pipelining that has a forwarding unit.

Suppose you had the following three instructions inside a large MIPS program:

add $$2,$$$1,$

or $$12,$$$2,$

and $$5,$$$6,$

Where would forwarding be needed in the code above? Explain using the above figure how the hazard would be detected. You can shade the requisite wires as part of your explanation.