The government of a large city needs to determine whether the city's residents will support the construction of a new gymnasium. The government decides to conduct a survey of a sample of the city's residents. Which one of the following procedures would be the most appropriate for obtaining a sample of the city's residents?

a) Survey a random sample of the employees and inmates at the old jail.
b) Survey every fifth person who talks into the City Hall on a given day.
c) Survey a random sample of persons within each geographic region of the city.
d) Survey the first 200 people listed in the city's telephone directory.