As a member of the City Council, you have been invited to address the city’s bicycling club about the mayor’s plan to create additional bike routes. The most important demographic factor you should consider when analyzing your audience is probably its

group membership

Explanation:

Based on the scenario being described within the question it can be said that the most important factor to consider would be it's group membership. Meaning which individuals are coming together as a group to take part in these discussions, which would allow you to observe and analyze what position the majority of the audience is taking.

Members of the bicycling club ( group membership )

Explanation:

The Members of the bicycling club are the most important audience that you are supposed to address when invited as a member of the city council to address the city's bicycling club, because the members of the bicycling club are people who will be affected most when the Mayor creates additional bike routes in the city so they should be the most important demographic factor to be considered at the address.

other demographic group to be considered are regular bikers who ain't members of the bicycling club and also citizens living around where these additional bike routes will be created.