Theorie:

Study the information about the indefinite article.
 
1. We use the article a/an with singular countable nouns when we talk about things in general.
 
A plane is more comfortable than a train.
  
A baker sells bread, cakes, pies.
  
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An is used when the word starts with vowel sounds a, e, i, o, u.
 
Wichtig!
an umbrella
  
a university
 
2. We can use a/an after the verbs to have and to be.
 
She is a photographer. She has a camera.
  
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3. We can use both a/an and the before a singular countable noun to represent a class of people, animals, things.
 
A/The dolphin is more intelligent that a/the shark.
  
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We do not use a/an with uncountable or plural nouns.
 
Would you like some tea?