Here's a problem to solve: The Milky Way is a part of 30 or more galaxies called the Local Group. Which would be the most likely reason these galaxies are considered to be part of the Local Group?

Among the 4 following options, which is the correct answer?

- A: They are all the same type of galaxy.
 
- B: They all have the same number of stars.
 
- C: They are all attracted to each other by gravity.
 
- D: They can all be seen without the aid of a telescope.
 