Which of the following statements is true with regard to the light reaction of photosynthesis?

• A
  In $PS-II$,the reaction centre chlorophyll-$\alpha$ has an absorption peak at $680 \; nm$,hence it is called $P_{680}$.
• B
  In $PS-I$,the reaction centre chlorophyll-$\alpha$ has an absorption peak at $700 \; nm$,hence it is called $P_{700}$.
• C
  The splitting of water molecules is associated with $PS-II$.
• D
  Photosystems-$I$ and $II$ are involved in the $Z$-scheme.