What are some functions of the european union?

The overall function of the European Union is to create and implement laws and regulations that integrate the member states of the EU.  The countries of the EU are supposed to have uniform laws and policies concerning a variety of things (like immigration, labor, weights and measures -- all sorts of things).  The function of the EU government is to decide how this integration should be done and to carry it out.

For example, 16 members of the EU use the Euro as their currency.  One of the functions of a part of the EU government was to devise the currency -- to decide what it would be called, what it would look like, etc.  Another part of the EU government tries to get countries using the Euro to enact fiscal policies that will keep the Euro stable.  They try, in other words, to prevent fiascos like what happened in Greece this past year and they try to remedy them if they happen.

a and b because with the other three, they simplify to something else.