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 $3$ and $4$ are solved by:

Select one:

a$.$ stall only

b$.$ stall and forwarding from Ex in $3$ to ex in $4$

c$.$ forwarding from mem in $3$ to ex in $4$ then stall

d$.$ stall and forwarding from mem in $3$ to ex in $4$

e$.$ forwarding from mem in $3$ to mem in $4$