Consider three widely separated galaxies in an expanding universe (look at picture below). Imagine that you are located in galaxy 1 and observe that both galaxies 2 and 3 are moving away from you. If you asked an observer in galaxy 3 to describe how galaxy 2 appears to move, what would he or she say?

hi... I won't be able to give you a detailed explanation but here's as far as i know:

If you ask someone in galaxy 3 how galaxy 2 appears to move, they'd say that it seems to move away from them too.

Explanation:

Our universe is constantly expanding, right? But there is no central point in the whole expansion thing. A common example used to describe this is a balloon being blown up. Imagine there are little dots on the balloon. When the balloon is blow up, the dots seem to move away from each other but there isn't any one that stays where it is. So that's kind of like the universe.

Galaxy 3 will see galaxy 2 move away from it too.

I don't know a lot about this so please correct me if I'm wrong but... hope this helps.

the answer is b, have negligible mass

where’s the list ? the question is incomplete