$($a$)$ Explain why pyridine A undergoes electrophilic substitution of hydrogen much less readily than benzene. Draw a mechanism for the reaction below to show why the electrophile enters in the $3-$nosition.

$($b$)$ Draw mechanisms to explain why furan $B$ gives $2-$bromofuran on bromination in an inert solvent, but gives a completely different compound in methanol.

$($c$)$ Explain why pyrrole $C$ undergoes electrophilic substitution of hydrogen much more readily than pyridine $A.$ Explain why pyrrole is selectively brominated at $C-2$ by $N-$bromosuccinimide $($a mild source of $B{r}^{+}$