Compounds Containing Nitrogen

Aniline on treatment with $\text{NaNO}_2$ / HCl at about $0^\circ\text{C}$ gives a compound A, which on further treatment with CuCN / KCN gives a compound B, which when reacts with $\text{H}_2$ / Ni gives a compound C. The compound C on reaction with $\text{HNO}_2$ gives a compound D. The structure of D is: