Answer:
D. It's the right answer.
Step-by-step explanation:
This is not very difficult to know that:
"The author compare to the process of photosynthesis in plants " means that the the use of solar farms to power cities is comparable to Photosynthetic cells (solar farms) power entire cities (whole leaves or stems though these "convertors" (CELLS) in order to provide power to the whole plants( cities) for the FUTURE POTENTIAL SOURCE OF POWER IN THE WORLD.