Given below is the diagram of a stomatal apparatus. In which of the following are all the four parts labelled as $A, B, C$ and $D$ correctly identified?

• A
  $A$-Subsidiary cell,$B$-Epidermal cell,$C$-Guard cell,$D$-Stomatal aperture
• B
  $A$-Guard cell,$B$-Stomatal aperture,$C$-Subsidiary cell,$D$-Epidermal cell
• C
  $A$-Epidermal cell,$B$-Guard cell,$C$-Stomatal aperture,$D$-Subsidiary cell
• D
  $A$-Epidermal cell,$B$-Subsidiary cell,$C$-Stomatal aperture,$D$-Guard cell