$($i$)$ Identify A and provide a mechanism to account for its formation.

i$).$

ii$).KCN$

$C_{10}{H}_6{N}_2$

$3$

A

$($ii$)$ Identify $B$ and provide a mechanism to account for its formation.

i$).n-$BuLi

ii$).C{O}_2$

$C_9{H}_6{O}_{2}S$

iii$).H^{o+}$