$A$: The first circulatory system is observed in the phylum Annelida.
$R$: The first true coelom is observed in the phylum Annelida.

• A
  Both $A$ and $R$ are true.
• B
  Both $A$ and $R$ are false.
• C
  $A$ is true and $R$ is false.
• D
  $A$ is false and $R$ is true.