Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: $A$ reaction can have zero activation energy.
Reason $R$: The minimum extra amount of energy absorbed by reactant molecules so that their energy becomes equal to threshold value,is called activation energy.
In the light of the above statements,choose the correct answer from the options given below:

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