Assertion $(A)$: Organisms of the same species cannot interbreed.
Reason $(R)$: Fertilization occurs to form a zygote.

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