Explanation:

- Option 1: 13 September

- This date is not recognized as the International Day of Democracy.

- Option 2: 14 September

- This date is also not associated with the observance of the International Day of Democracy.

- Option 3: 15 September

- The International Day of Democracy is observed on 15 September. It was established by the United Nations General Assembly in 2007 to promote and uphold the principles of democracy.

- Option 4: 16 September

- This date does not correspond to the International Day of Democracy observance.

- Option 5: None of the above

- Since the correct answer is included in Option 3, this option is not applicable.