Which of the following is a Stephen reaction?

• A
  $R-C(=O)-R + 4[H] \xrightarrow{Zn-Hg/\text{conc. } HCl, \Delta} R-CH_2-R + H_2O$
• B
  $R-CH=O$ $\xrightarrow{H_2N-NH_2, -H_2O} R-CH=N-NH_2$ $\xrightarrow{KOH/\text{ethylene glycol}, \Delta} R-CH_3 + N_2$
• C
  $R-COCl \xrightarrow{H_2, Pd-BaSO_4} R-CHO + HCl$
• D
  $R-C \equiv N + 2[H]$ $\xrightarrow{SnCl_2/\text{dil. } HCl} R-CH=NH \cdot HCl$ $\xrightarrow{H_3O^+} R-CHO + NH_4Cl$