Find the mistakes in the following sentences .Identify the mistakes , explain why they  occurred and  write the correct forms.

a)John has broken his arm.
  This has happened  yesterday .
b)My brother is not at home.
  He didn't come home yet.
c)Have you written the greeting card? 
  Yes,I did.
d)When did you last see him ?
  I have seen him yesterday.




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