ARTICLES
Indefinitive articles are 'a' and 'an'

1. 'a' used with singular countable nouns that begin with a constant sound.

• example : All that is needed is a computer and a telephona line ( line 3 ).

   2.  'an' used with singular countable nouns that begin with a vowel sound or with the  
        silent 'h'.

• example : An example of this was when an unidentified source ( line 16 ).

Definitive article are 'the'
is used with the following :

•  to refer to a specific person or object
•  to refer to superlatives
•  to refer to something or someone a second time
• to refer to something that is only one of its land
• to refer to a special class of people
• to refer to continues that begin with united or republic
• to refer to a range of mountains, group of islands, names of rivers.
• example : The information from the Net ais numerous individuals and organisations ( ine 5 ).