The relationship between photosystem I (PSI)and photosystem II (PSII)is correctly described by which of the following statements?

A)PSI precedes PSII in photosynthesis.
B)Electrons are excited by PSI or PSII,but not both.
C)Chlorophyll molecules in the reaction centers of PSI and PSII are designated P700 and P680,respectively,to reflect the wavelengths of their light absorption maxima.
D)PSII was discovered before PSI.
E)Only PSI contains a special pair of chlorophyll a molecules.