Assertion $A$: $A$ patient suffering from malaria experiences chills and high fever.
Reason $R$: The rupture of red blood cells by the $Plasmodium$ parasite releases a toxic substance called haemozoin into the blood.

• 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.