$A$: Yeast is included in the kingdom of multicellular decomposers.
$R$: Fungi exhibit parasitic or saprophytic modes of nutrition.

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