Many Cities Have Created Non-Emergency Phone Numbers That Citizens Can $$+$$

Many cities have created non-emergency phone numbers that citizens can call with questions or comments about public services .However, complaints about government services may rise just because complaining is easier .In cities with very low service quality, that relationship may not be as strong because citizens were already making a lot of complaints through other means .On the other hand, citizens often appreciate the non-emergency phone number service, which can improve local government's reputation, and in turn, decrease the number of complaints about government .Other factors, of course, affect the number of complaints besides the non-emergency phone number .For example, news coverage of local government affairs may raise awareness of particular issues and generate additional complaints. A foundation interested in local government affairs developed a logic model and research design to test these hypotheses .The foundation wanted to find out whether the rate of citizen complaints about local government was higher in cities with non-emergency lines, and whether the number of complaints increased after cities adopted non-emergency phone numbers.
$$+$$ What is the unit of analysis in this model?

A) Cities
B) Individuals
C) Complaints
D) Quantitative