Using BF as the reflective points, A will become C and G will become E. It also works the other way around: C becomes A and E becomes G.
You would be helped if you could actually try it. If you put a mirror on BF and look first at A and G and then move so you can see C and E you should be convinced of the reflective property. Then turn the mirror around and look again.
These things look to be quite simple but it took many centuries before they were properly explained, and even then there were difficulties.
The second choice does not work at all. You cannot see any reflection the way you can with the first choice.
