Question

3. Which of the following characteristics was required to be a citizen of Athens? nobility

Answer 1

This is a strange question as by far the most important thing among these was that citizens of Athens were people who were at least 18 years of age together with the fact that they were born in the city of Athens itself. Considering, these are the most important criteria, we can conclude that from the list of your possible answers having a grandfather who was a citizen is probably the closest one because it basically means that he was already born in Athens which makes it highly probable that you were born in Athens as well. 

Answer 2

You needed to be:free man, male, born in Athens of a married couple born also in Athens.