This would be the legend!
The legend of a map tells you for example that a square means a capital city.
A scale shows you how big things presented on the map are in real life and the compass helps you orient the map with respect to the North.
A title helps you understand what the map focuses on (for example: " A Political map of Italy").
The cause is the fact that they have orbits of different size.
For two objects in orbit around the same central body, the one in the
larger orbit will take longer for each complete revolution.
And if two objects are in the same-size orbit, their periods of revolution
are identical, even if the objects have different size and mass.
(Example: All TV satellites are in the same orbit. Some are big and heavy,
some are smaller and lighter, but all of them revolve around the Earth in
exactly 24 hours.)
According to NASA the only one of these that actually seems to be a real type of galaxy would be C. Barred Spiral Galaxy. I hope this helps :)
Earth would float and everyone would die
