$A$: Reticulate venation is observed in the leaves of sunflower.
$R$: Sunflower is included in the class Dicotyledonae.

• A
  $A$ and $R$ are both true, and $R$ is the correct explanation of $A$.
• B
  $A$ and $R$ are both true, but $R$ is not the correct explanation of $A$.
• C
  $A$ is true and $R$ is false.
• D
  $A$ is false and $R$ is true.