Consider achieving the best performance for the following instructions:

$1$ Add R$4,$ R$2,$ R$3$

$2.$ SW R$5,$ #$100($R$4)$

$3.$ LW R$6,$ #$200($R$4)$

$4.$ Sub R$7,$ R$5,$ R$6$

the data hazard between $1$ and $3$ are solved by:

Select one:

a$.$ forwarding from mem in $1$ to Ex in $3$

b$.$ forwarding from Ex in $2$ to Ex in $3$

c$.$ forwarding from Ex in $1$ to Ex in $3$

d$.$ no forwarding is needed

e$.$ forwarding from Ex in $1$ to mem in $3$