How might several countries all described as federations differ in practice? Some may have smaller units of government like states or provinces while others do not. The state governments may vary in amount of power shared with the central government. Some have a central government that makes decisions for the country while others do not. The state governments could be sovereign governments that do not share power as a central body.
"The state governments may vary in amount of power shared with the central government" would be the best option from the list, since all federal systems share power, but the extent of that power share is often different.
