$A$: The gametophytic plant body of bryophytes is a thallus.
$R$: The gametophytic stage of bryophytes is haploid and autotrophic.

• 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.