Let's rewrite the sentences using the correct forms of "is," "isn't," "am," and "am not":
London aren’t a country.
London isn't a country.
The United States aren’t a city.
The United States isn't a city.
An elephant am not a small animal.
An elephant isn't a small animal.
English and Turkish isn’t sister languages.
English and Turkish aren't sister languages.
Mercedes aren’t a bike.
Mercedes isn't a bike.
Is I a student ?
Am I a student?
Mrs. Stuart aren’t a poor woman.
Mrs. Stuart isn't a poor woman.
Cigarettes isn’t good for people.
Cigarettes aren't good for people.
The North Pole am not hot.
The North Pole isn't hot.
Simon are from United Kingdom.
Simon is from the United Kingdom.
In each case, the subject-verb agreement was corrected by ensuring that the singular or plural form of "is" and "are" was used appropriately. Additionally, the correct form of "am" was used for the first person singular.