Identify the sentence in which the bold word functions as an adjective.
a. the proportion of people who live in a city has increased over time.
b. city planners work to design urban spaces to best serve the needs of various community stakeholders.
c. while some people prefer the bustle of living in a large city, others thrive in smaller communities.
d. it can be difficult to decide whether to pursue a job opportunity in an unfamiliar city.