Assertion $(A)$: $Fucus$ shows a diplontic life cycle.
Reason $(R)$: In $Spirogyra$,the diploid zygote is the dominant and active stage.

• A
  Both $A$ and $R$ are true,and $R$ is the correct explanation of $A$.
• B
  Both $A$ and $R$ are 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.