$S$: Thermoacidophiles survive in acidic and high-temperature conditions.
$R$: Archaea can survive in extreme conditions.

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