$S$ (Assertion): Alexander Fleming established the full potential of penicillin as an effective antibiotic.
$R$ (Reason): Alexander Fleming discovered penicillin.

• 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,but $R$ is false.
• D
  $S$ is false,but $R$ is true.