Using 'a' or 'an'

'A' and 'an' mean 'a (any) one' but 'the' refers to someone or something already known.
Can I have a cake?
Can I have the cake with the cherries?

We use 'a' and 'an' when:
We mean one of many and not a special one.
Can you lend me a pen? - Have you got a car?

When we give a person's occupation.
She's an architect.

In fixed expressions such as:
have a rest    make a mistake        go for a walk             in half an hour         a lot of time

Use 'an' when the next word starts with a vowel sound:
an apple        an egg            an Indian       an orange      an umbrella               an hour
however:
a European   a ewe             a union          a Eurasian    a hotel            a one-way street

Put 'a' or 'an' in the following:

• 1) A male sheep is called a ram, and a female one is called __ ewe.
  
  a
  an
  
  
• 2) You spelled 'after' without __ 'r'.
  
  a
  an
  
  
• 3) Mr Smith is __ honest man so I would give him the job.
  
  an
  a
  
  
• 4) __ 18-year-old man was arrested for the bank robbery of six months ago.
  
  a
  an
  
  
• 5) I go to __ university in Italy.
  
  a
  an
  
  
• 6) If you're not busy we could go for _ walk.
  
  a
  an
  
  
• 7) I have been working for __ European company for ten years now.
  
  a
  an
  
  
• 8) John's __ waiter in a high class restaurant.
  
  an
  a