[bad word] /www.bbc.co.uk/worldservice/learningenglish/radio/specials/1456_gramchallenge24/
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Nuala's Grammar Explanation:
Definite articles:

Today we're looking at articles; the words 'a' 'an' and 'the' and we're concentrating on the
definite article 'the'. Let's look at [bad word] 
Firstly, to refer to something or someone both speakers in a conversation know about:
Helen: Have you got any kids?
Diarmuid: Yeah, a girl and a boy. The girl's 10 and the boy is 7.
At the beginning of the sentence, Diarmuid says 'a' girl and 'a' boy because this is the first
time he's talking about his children. Later he says 'the girl' and 'the boy' because now Helen
knows which children Diarmuid is talking about.
Secondly, we use 'the' before seas, rivers, and groups of mountains or islands.
Example 1: the Atlantic
Example 2: the Nile
Example 3: the Himalayas
Example 4: the Philippines
Thirdly, we use 'the' if there is only one of these people or things:
Example 1: the BBC
Example 2: the Taj Mahal
Example 3: the moon
And finally, we use 'the' before superlative adjectives
Example 1: the smallest
Example 2: the prettiest
Example 3: the most expensive
So to recap, we use 'the' when both the speaker and listener know about the person or
thing being discussed, before the names of some areas of geography, if there is only one of
these people or things and before superlative adjectives.
That's all from me, good luck with your grammar challenge!
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