Article use in English – a/an, the or zero article

Some advanced points for definite and indefinite articles:

Classes (formal):  The tiger is threatened with extinction.

To name a work by an artist: My mother found a  Salvador Dali in the attic.

National groups: The Irish are known to be great writers and drinkers.

In measurements ‘a/an’ can be used instead of ‘per’: If petrol costs €1 a litre and your car is travelling at 50 miles  an hour,  how much will it cost to drive for 10 miles?

Some plural political/music/other groups: The government is evenly divided between the