I think the answer is A. As for C, Anthocyanins are located in the vacuole and their light absorption does not affect the process of photosynthesis which occurs in the chloroplast. Anthocyanins do participate in prevention of High-Light Stress (or Photoinhibition) but they have no role to play in gathering light energy for photosynthesis. Therefore, to improve the quantum efficiency (quanta of light per CO₂ molecule fixed or O₂ evolved, or any other quantifiable photochemical event) of the light reaction, anthocyanins play no role.
But, if there are more chlorophyll molecules per reaction centre, i.e. there is a greater number of chlorophylls in the LHC (Light Harvesting Complex), or the Antennae system, then the quantum efficiency can be improved, the absorption band widened and thus the light compensation point is reached earlier. The extra molecules of chlorophyll absorb energy at their specific wavelengths of light and transmit this energy to the main reaction centre by FRET(Fluorescence resonance energy transfer). Therefore, greater the number of chlorophylls per reaction centre, greater is the light energy absorbed and transmitted to the reaction centre and hence, better is the quantum efficiency.
More technically, having more chlorophylls open up more pathways for photochemical energy quenching, and thus improves the efficiency by minimizing fluorescent losses.