$A$: $Pinus$ is known as a gymnosperm.
$R$: In $Pinus$,the ovules are not enclosed by any ovary wall and remain exposed.

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