Answer:B.Hubble's constant
Step-by-step explanation:
Astronomers have come up with the most precise measurement to measure the expansionof the universe.
We know the space is expanding and the push behind the swelling of the space is measured by a constant called the "hubble's constant" and it is measured in kilometers per second per megaparsec.
It is a way to measure distance between two stars but scientists think it is not accurate enough and are still looking for more specific and precise measurements