Chlorophyll absorbs light primarily in the blue and red wavelengths and reflects green light, which is why it appears green. If chlorophyll were red instead of green, it would likely absorb light in the green and blue wavelengths while reflecting red light.
To produce the lowest rate of photosynthesis, you would expect it to absorb the least amount of light. Since red chlorophyll would reflect red light, this would mean that the plant would absorb less red light.
Therefore, the answer is:
C. red