Assertion $(A)$: Viruses are considered as a link between living and non-living things.
Reason $(R)$: Viruses are inactive and behave like non-living matter in a free state,whereas they show active and living behavior inside a host cell.

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