Теория:

Study information about the definite article.
 
We use the in these situations:
 
1. nouns are unique.
 
Haven't you been to the Acropolis yet?
  
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2. names of cinemas, museums, hotels, theatres, newspapers, ships.
 
I want to go to the Odeon.
  
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3. names of rivers, seas, groups of islands/states, mountain ranges, deserts, oceans.
 
The Thames is the longest river in England.
  
Thames.jpg
 
4. names with of.
 
The Tower of London is the most wonderful sight.
  
5. musical instruments.
 
Can you play the piano?
  
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6. names of people/families/nationalities in the plural.
 
The English are considered to be reserved.
 
7. titles without proper names.
 
The Queen, the President
  
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8. adjectives used as plural nouns.
 
the rich, the poor
 
9. the superlative degree of adjectives/adverbs.
 
She is the friendliest person I've ever met.
  
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10. when it is clear which thing or person we mean.
 
Can you tell me the time, please?
Источники:
vgreciju.ru
www.spv-uk.co.uk
bakerstreet.wikia.com
www.youmatter.suicidepreventionlifeline.org
www.sodahead.com
www.psychologos.ru