Galileo's moon studies.
Answer: Option B.
Step-by-step explanation:
Galileo studied about the moon. At that time, the scientists thought that the surface of the moon is very smooth but it was Galileo who discovered that the surface of the moon was not smooth.
He discovered that the moon had small pits which made it's surface rough. The moon has mountains and other features also just like the features of the planet Earth, this was also discovered by Galileo. Along with this he made startling discoveries about Jupiter also.