I'll start by listing why the other ones are incorrect.
B- A national banking system.
The government isn't a bank anymore. It used to have a national bank, but government is much more than that.
C-Basic unit of currency used by the European union
The government isn't a type of money.
D-the ability to deal with situations and issues without provoking hostility
The government has this ability, but that's not what government is.
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Correct:
A-A form of system of rules.
This is the basic definition of government.
Hope this helps!
;)
