The statements that describe a key characteristic of Athenian democracy are:
A) All free males over 18 born to Athenian parents were citizens: Only adult males who were citizens and Athenians, and who had finished military training as ephebes, had the right to vote in Athens. This excluded a majority of the population: slaves, children, women and metics.
Athenian citizens must be legitimate descendants of other citizens, and after the reforms of Pericles and Cimon in 450 BC, children of an Athenian father and mother, except for the children of Athenian men and foreign women.
B) All citizens served in the Assembly: The central events of the Athenian democracy were the meetings of the Assembly (Ekklesia). Unlike in a Parliament, the members were not elected, but were citizens who could attend whenever they wanted. The democracy created in Athens was direct, not representative as it is today: any adult male who was a citizen and over 18 years of age could participate, and it was a duty to do so.
D) The Council of Athens carried on the daily business of the city: The role of the Council of Athens was to collect the proposals of citizens' law, the probouleuma (προβούλευμα), in order to establish the agenda of the sessions of the Ekklesia that it called. There was no competition between these two institutions.
In addition, the Council was in charge of verifying that the laws and decrees promulgated by the Ekklesia, which were often amended probouleuma, could not go against the fundamental laws of the city.