Answer:
D. The shape of galaxies in cluster galaxies
Step-by-step explanation:
When the Universe began to expand, everything present in Universe began to move at a very high rate. This was concluded that some external force is working on it in order to pull these things. It was known as the dark energy.
Thus the size and shape of galaxies is increasing because of this dark energy, hence the study of change in shape and size of galaxy gives information about dark energy as it is constantly applying force thus increasing the size.