Identify the compound $A$ and $B$ in following reaction.

• A

  $\mathrm{A}=$ methylisocyanide, $\mathrm{B}=$ Methanoic acid
• B

  $\mathrm{A}=$ Ethanenitrile, $\mathrm{B}=$ Methanoic acid
• Correct answer
  C

  $\mathrm{A}=$ Ethanenitrile, $\mathrm{B}=$ Ethanoic acid
• D

  $\mathrm{A}=$ methyl cyanide, $\mathrm{B}=$ methanoic acid

Hence, the correct answer is option: 'C'.