Assertion $(A) :-$ The whole scheme of transfer of electrons starting from $PS-II$ to $NADP^{+}$ is called $Z-scheme$.
Reason $(R) :-$ When all the carriers of this scheme are placed in sequence on a redox potential scale,they appear like $Z$.
In the light of the above statements,choose the correct answer from the options given below:

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